Help trying to understand Pixelbot

Hi I'm new to autoit but i seem to understand it cause its not that hard, and i'm trying to make a pixel bot... i've been searching for some examples and i seem to be getting it but i still have some problems. i
don't understand this line

Opt("PixelCoordMode", 0)

i really just want to know what the OPT stands for cause i don't see it in the help file for autoit. Thanks in advance. ^^

AutoItSetOption ( "option" [, param] ) or Opt ( "option" [, param] ) example:

Opt("PixelCoordMode", 1) ;1=absolute, 0=relative, 2=client