It totals up all your auction's bids and buyouts if they are all sold in a little frame at the bottom of the auction tab.
/ap - Shows the list off all 3 slash commands (below)
/ap Cut - Toggles the Auction House Cut on or off
/ap BO - Toggles Buyout Total on or off
/ap Bid - Toggles Bid Total on or off
/ap Sold - Include/Exclude sold auctions in the totals