Every term, plainly defined.

Opta has affiliate relationships with Coinbase, MEXC, Bitso, and Wise. These exchanges pay Opta a small commission when a user signs up via an Opta link. The full list is published at /disclosures. Affiliate status is a separate field from ranking, the ranking is always total-cost-ascending, never affiliate-first. Every affiliate link is labeled inline so you know.

Traditional exchanges match buyers and sellers on an order book. AMMs ("automated market makers") replace the order book with a liquidity pool, anyone can deposit two assets, and a math formula determines the rate based on the pool's balance. The rate moves automatically as the balance shifts. Uniswap, Curve, Balancer are AMMs. Better for thin pairs (always tradeable, even at small size) but worse for tight spreads (the formula has built-in slippage).

Opta's API will let developers query the same data the website surfaces, best-route, full path comparison, accuracy variance, corridor history. The plan is API-first eventually so partner apps (wallets, finance dashboards, treasury tools) can embed Opta's index. Beta now; public API and docs ship after launch.

Benchmarks are the "what's the conventional alternative?" reference. Wise (formerly TransferWise) is the modern fintech benchmark; Bank Wire (SWIFT) is the legacy benchmark. Both produce a "you receive" number Opta surfaces alongside the live exchange rankings. If the cheapest crypto route saves you 4% over Bank Wire, that's the savings number Opta shows.

Order books are stacks of bids and asks. The bid-ask spread is the gap at the top, the cost of crossing from one side to the other. When you market-buy, you're matching against the best ask; when you market-sell, you're hitting the best bid. "Mid-market" is the average of the best bid and best ask. Tight spreads = liquid market; wide spreads = illiquid.

When a direct pair doesn't exist or has bad liquidity, the route bridges through a third asset. Stablecoins are the most common bridges because they hold 1:1 peg to USD and trade against everything. Opta's path-finder picks bridges that minimize total cost, usually USDT for crypto-to-fiat, USDC for crypto-to-crypto.

CEXs are the traditional model. You sign up, complete KYC, deposit money, and trade against their order book. They hold custody of your assets while they're on the platform. Fast, deep liquidity, fiat rails, but you trust them with your funds, and they can freeze accounts or fail (like FTX did). Opta indexes 30+ CEXs.

A corridor is a single source-asset / destination-asset pair. Opta indexes corridors as the unit of analysis, every corridor has its own page, its own ranked exchanges, its own historical accuracy data. Some corridors are direct (USDC→BRL on Bitso); others require multi-hop routing through an intermediate asset.

DEXs don't require an account, KYC, or custody handoff. Swaps happen wallet-to-wallet via smart contracts, paying gas to the blockchain. Most DEXs are AMMs (Uniswap, Curve), some are aggregators that route across multiple AMMs (1inch, LI.FI). DEXs handle crypto-to-crypto well; for fiat off-ramps you still need a CEX or a fiat rail.

AMMs need a deterministic formula to set prices as their liquidity pool balance changes. The constant-product curve (x*y=k, used by Uniswap) prices well for most pairs but slips more for stablecoin trades. The stable-curve (used by Curve.fi, hence the name) is mathematically optimized for assets that should trade near 1:1, far less slippage on USDC/USDT or USDC/DAI swaps. Different curves serve different pairs.

An exchange is the venue where conversions happen. CEXs (Binance, Coinbase, Bitso, Kraken) hold your funds and run an order book. DEXs (Uniswap, Curve, 1inch) are smart contracts on a blockchain that swap assets without holding them. Opta indexes both: every CEX in the registry, plus DEX aggregators (LI.FI, 1inch) for the on-chain side.

Fees are the visible part of conversion cost. They show up on the receipt: maker/taker fees on order books, withdrawal fees on the way out, deposit fees on certain rails. Fees alone don't tell the full story, a "0.10% fee" with a 0.8% spread costs more than a "0.40% fee" with no spread. That's why Opta ranks by total cost, not by fee alone.

Fiat is the technical term for traditional money, issued by a central bank, not backed by a commodity, accepted as legal tender. The opposite of fiat in this context is crypto. Opta indexes conversions across both: fiat-to-crypto, crypto-to-fiat, and fiat-to-fiat (via Bank Wire and Wise benchmarks).

Gas is what you pay the blockchain itself to validate and record your transaction. It's denominated in the chain's native token (ETH for Ethereum, SOL for Solana, MATIC for Polygon). Gas costs vary with network congestion, peak hours can cost 10x off-peak. Stablecoin transfers on Solana or Polygon often have gas under $0.01; the same on Ethereum during a busy day can hit $10 or more.

A liquid pair has tight spreads and lots of resting orders, so trades don't push the price around much. Thin pairs have wide spreads and shallow books, converting a large amount can move the price against you (slippage). Opta shows liquidity signals on every result row so you know whether the rate you're seeing is realistic for your size.

Margin trading lets you control more value than you own. If you have $1,000 and use 5x leverage, you trade as if you have $5,000. If the market moves your way, gains are 5x; if it moves against you, losses are 5x, and if losses hit your collateral, the position is automatically liquidated. Opta does not index margin trades, every route is spot, no leverage. Margin is a separate world (perp DEXs, futures exchanges).

The mid-market rate is what financial newswires publish ("EUR/USD: 1.0850"). Nobody actually transacts at this rate, exchanges quote a spread around it. It's useful as a reference for measuring how much spread you're paying. Opta uses BCB's PTAX rate (the official Brazilian central bank fixing) as the mid-market reference for USD/BRL.

Some pairs aren't traded directly. ETH→BRL on a smaller exchange may not exist, but ETH→USDT and USDT→BRL both do. Opta finds these multi-hop routes automatically and prices them end-to-end (including the inter-exchange transfer fees if the hops cross venues). Multi-hop costs more than direct because each hop has its own spread + fee, but is sometimes the only way to get from A to B.

When you withdraw crypto from an exchange to a wallet, or move crypto between wallets, you pay a fee to the network's validators. On Bitcoin and Ethereum it's called gas; on other chains it's just a network fee. The fee depends on chain congestion and transaction complexity. Stablecoin transfers on Solana, Polygon, or BSC are pennies; the same on Ethereum mainnet during peak hours can hit $10 or more.

An order book is the engine that exchanges run on, every limit order from every trader, sorted by price. The top of the book is the best available price; the depth below tells you how much volume is sitting there. Order-book exchanges (Binance, Coinbase Pro, Kraken, Bitso) publish their books publicly; retail conversion surfaces ("Coinbase Convert", quick-buy widgets) are layered on top and often hide the real spread.

P2P platforms (Binance P2P, LocalCoinSwap, Paxful) match buyers and sellers directly. The platform escrows the crypto while the fiat payment happens off-platform, bank transfer, cash, mobile money. Slower than a CEX, often with wider spreads, but works in countries where exchanges can't operate (Venezuela, certain ARS scenarios) or where bank rails are restricted.

A rail is the plumbing for a fiat transfer. PIX is Brazil's instant rail (free, seconds). SEPA is the EU's rail (free in-zone, minutes-to-hours). ACH is the US rail (free-ish, 1–3 business days). SWIFT/Bank Wire is the international fallback (expensive, 2–5 days). Different rails have different cost-time-reach tradeoffs, and your destination currency dictates which ones apply.

Rates change continuously as supply and demand shift. The number you see on Opta is the rate the engine quoted when it priced the route. Time matters: a rate from 60 seconds ago may not be the rate you execute at. That's why every Opta page is timestamped and refreshes.

Reference rates come from independent authorities, not exchanges. PTAX is the official USD/BRL fixing published by Brazil's central bank twice daily; the European Central Bank publishes EUR fixings; the Federal Reserve publishes the H.10 series. Opta uses these as the neutral mid-market against which exchange spreads are measured. When an exchange quotes a price that drifts more than 50 basis points from the reference rate, the accuracy audit flags it.

Most exchanges offer a friendly "Convert" or "Quick Buy" surface, pick source, pick dest, see one number, click confirm. These hide the spread inside the rate they show you. The same exchange's order book, accessible elsewhere, often gives you a much better rate. Opta surfaces retail conversion costs as a range (the spread can be 0.5–1.2% wide on the same trade) so you can see what you're really paying.

Order books are stacks of orders at different prices. A small trade fills at the top of the book; a large trade has to walk further down, getting worse prices as it goes. Slippage is the difference between the price you saw and the average price you actually got. Thin pairs slip dramatically; deep pairs barely slip at all.

Spot trading means "buy this, get it now, settled at today's price." It's the simplest form of trade. The opposite is margin trading (borrowing to amplify your position) or futures (an agreement to buy/sell at a future price). Almost all of Opta's indexed routes are spot, no leverage, no derivatives. When you see "spot rate" or "spot price," it means the current cash market.

Every exchange quotes two prices for the same pair: a buy-side and a sell-side. The spread is the gap between them, expressed as a percentage of the mid-point. Tight spreads (under 0.1%) signal deep liquidity and active market-making; wide spreads mean you'll lose more crossing the book even if the advertised "fee" is zero. Spreads change second-to-second based on supply, demand, and order-book depth.

USDC, USDT, and DAI are all stablecoins pegged to the US dollar. Their value barely fluctuates against USD, which makes them useful as a "digital dollar" for cross-border conversions. You hold a stablecoin instead of a USD bank balance, then off-ramp directly to the destination currency. Opta treats USDC/USDT as USD proxies for benchmark math, but the real exchange rates can drift slightly off the peg.

Total cost is the only number that matters when comparing routes. It's the all-in delta between the mid-market rate and what you receive, expressed as a percentage. Every Opta result row shows total cost; every ranking is total-cost-ascending. Adverts talk about fees; Opta talks about total cost.

Variance is the gap between what was promised and what was delivered. Opta's accuracy audit, published at /accuracy, compares every exchange's quoted rate against its publicly executed rate at the same timestamp. Persistent drift earns the exchange a worse variance band; tight execution earns the green band. Variance is Opta's anti-puffery signal.

A wallet is the crypto equivalent of "your account at a bank", except you control the keys, not a third party. Self-custody (MetaMask, Trust Wallet, hardware wallets) means you alone hold the private key; if you lose it, the funds are gone, and nobody can freeze your account. Custodial wallets (your Coinbase / Bitso / Binance balance) are managed by the exchange, easier to recover, but the exchange can freeze your account or be hacked.