The word platform is used in several different contexts, usually referring to some kind of standing surface used to support things, give them stability, or visibility:
http://en.wikipedia.org/wiki/Platform

In computing, a platform describes some sort of hardware architecture or software framework (including application frameworks), that allows software to run.
http://en.wikipedia.org/wiki/Platform_%28computing%29

Platform is a pioneer and the global leader in High Performance Computing (HPC) management software.
http://www.platform.com/

Developers just like you have built applications on Facebook Platform that millions of people use everyday. Join our developer community and help make ...
http://developers.facebook.com/

Seattle gallery featuring contemporary painting, works on paper, photography, sculpture, installation, and media-based work.
http://www.platformgallery.com/