A contract, unit, or lot represents the standard trading size for a particular financial instrument. This standardization allows for efficient price discovery and trading by establishing uniform quantities for each market. For example, a standard stock option contract represents 100 shares, while a forex standard lot represents 100,000 units of the base currency.

Different markets have different contract specifications designed to facilitate trading while maintaining reasonable minimum transaction sizes. Futures contracts specify exact quantities (1,000 barrels for crude oil, 5,000 bushels for corn), while forex markets offer various lot sizes including standard (100,000), mini (10,000), and micro (1,000) lots to accommodate different trader sizes and risk tolerances.

Real-world example: A trader buying one crude oil futures contract on NYMEX controls 1,000 barrels of oil, so a $1 per barrel price movement results in a $1,000 profit or loss on the position.