Quick Glossary

The words this guide uses, in one page. The Reference Manual's Glossary has the full vocabulary.

Term	Meaning
Ask	The lowest price at which someone is currently willing to sell. Also called the offer.
Auction	A phase in which orders are collected and then all matched at once, at one price (the equilibrium price). Used to open and close the day.
Bid	The highest price at which someone is currently willing to buy.
Circuit breaker	A risk control that halts trading in a symbol after a large, fast price move.
Configuration	The YAML file that describes the whole exchange: symbols, participants, timetable and rules. It is deployed before the exchange uses it.
Drop copy	An independent copy of every fill, sent to risk and compliance systems.
Engine	pm-engine, the one process that owns the order books and matches orders.
Fill	An execution: part or all of an order traded.
Gateway	A process through which participants connect, or the connection itself. The participant ID is also called the gateway ID.
Limit order	An order with a price limit: buy at that price or lower, sell at that price or higher.
Maker / taker	The maker's order was resting in the book; the taker's order arrived and traded against it.
Market maker	A participant whose job is to quote both a bid and an ask, so others can always trade.
Market order	An order without a price: trade now at the best prices available.
Order book	All resting buy and sell orders for one symbol, best prices first.
Participant	A trader, market maker or operator configured to connect, with an ID such as TRADER01 and a role.
P&L	Profit and loss. Realized P&L is locked in by closing a position; unrealized P&L is what an open position would make at the last price.
Position	How many shares a participant holds: positive is long, negative is short.
Price-time priority	The matching rule: better prices first; at the same price, earlier orders first.
Resting	An order waiting in the book for someone to trade with it.
Session phase	Where the trading day is: PRE_OPEN, OPENING_AUCTION, CONTINUOUS, CLOSING_AUCTION, CLOSED.
Spread	The gap between the best ask and the best bid.
Symbol	A tradeable instrument, such as AAPL, with its own order book.
Tick	The smallest allowed price step for a symbol, for example 0.01.
Time in force (TIF)	How long an order stays active: DAY, GTC (good till cancelled), or only in an auction (ATO, ATC). IOC and FOK are order types, not TIF values.
ALF, BALF, CALF, RALF, LALF	EduMatcher's protocols: text order entry, binary order entry, market data, post-trade data and logging.