When a software product, usually a video game is being developed for multiple systems (ex. playstation 3, xbox 360.) the devloper will often create the product on one then create a port, or reformatted version for the other. The system that the software is developed for first is the lead platform.
"The lead platform for Dragon Age Orgins was the PC and ports were created for the PS3 and the X Box 360
by The_Darkness January 12, 2011