Good introduction to the various types of orders that can be used to enter or exit trades: from Wikipedia.
All order types—market orders, limit orders and stop orders— can be used to either enter or exit a position, to increase the size of an existing position, to reduce the size of an existing postion without closing it out completely (“taking partial profits”), and also to go long or to go short.
So, for example, a buy stop can be used either as a means to enter (or add to) a long position, or to exit (or reduce the size of) a short position.
Limit orders and stop orders are not perfectly inverse to each other: The constraint on a limit order prevents any trade from executing at any price worse than the one specified by the limit order. The constraint on a stop order prevents the trade from occurring unless and until price trades at or worse than the stop price, but does NOT constrain the price at which the trade will execute. The order type supported by some brokers (not all) that is perfectly inverse to a stop order is a “market if touched” order (MIT.) For an MIT order, the broker sends a market order to the exchange if price trades at or better than the specified price.
Orders can be linked together using two different types of constraints:
1) One Triggers Other (OTO): This constraint prevents contingent orders from being sent to the exchange by the broker unless and until the antecedent order has been filled. It is common to submit orders to enter a position as a triplet of the three orders: One order to enter the position, a limit order to exit the position at some price better than the entry price, and a third stop order to exit the position at a loss if the market goes against the trade by too much. The second and third orders should NOT be sent to the exchange or become “active orders” unless and until the primary order to enter the position is executed. So the three orders are grouped together as a unit, such that activation of the two orders to exit is contingent upon the successful execution of the initial order that establishes (or adds to) the position. Order triplets with a primary (antecedent) order to enter a position, and a stop loss and profit target order linked to the first one using the OTO (one-triggers-other) constraint are commonly called “bracket orders.”
2) One Cancels All (OCA): This constraint ensures that only one of the orders in a set of orders will be executed by cancelling all the other orders in the set immediately upon first execution of any of the orders in the set. It is common to link limit orders to exit at a profit target with stop orders to exit when the price moves too far against the trade using the OCA (one-cancels-all) constraint. Some brokers and trading platforms refer to this constraint as “one cancels other” (OCO.)