It stands for arrival price algorithm; a trading algo (trading algorithm) that is designed to minimize trading costs while achieving the bid/ask midpoint price at the time the order is placed, as framed and outlined by the user-defined level of risk aversion whereby the pace of the execution is preset, and so is the user-defined target percent of average daily volume. This algo uses randomization to keep the order concealed while continuously attempting to execute quickly.

The key parameters for this algo are max% average daily price (e.g., 1%, 5%, 8%, etc), risk aversion level (urgency), start time, end time, trading past end time, and attempt completion by end of day (EOD).