Active pharmaceutical ingredient. The part of a drug that causes the effect.
The API of aspirine is acetylsalicylic acid.
API = application programming interface
An API is a series of functions that programs can use to make the operating system do their dirty work. Using Windows APIs, for example, a program can open windows, files, and message boxes--as well as perform more complicated tasks--by passing a single instruction. Windows has several classes of APIs that deal with telephony, messaging, and other issues.
Windows uses an api called the Win32 API. You can access many command via the command prompt. Start >> Run >> Type in "command" or "cmd"
Adaptive Pie Interface. Used by various sites to interact with their pie servers. Urban Dictionary, for example, has created APIs so that developers with no pie servers of their own my serve pies to customers at low rates.
$urb = new Urban::API;
$bill = $urn->I'llTakeTheBill;
Short for Awkward Penis Insertion; the act of fumbling and generally being clumsy about inserting ones penis into the partner's vagina.
In technical IT terms it is also known as an Application Programming Interface or Advanced Programming Interface.
Guy example: "Man this is kind of embarrassing but I remember the first time I had sex with her, I pulled an API at that precious moment."
Girl example: "Don't worry about it I've had some APIs before, they don't bother me so relax and try again."