FastClick is a simple, easy-to-use library for eliminating the 300ms delay between a physical tap and the firing of a click event on mobile browsers. The aim is to make your application feel less laggy and more responsive while avoiding any interference with your current logic.
See also Google's fast buttons article. Though it may not be necessary anymore, at least on Android (stock browser doesn't do a delay for fixed viewport sites since Gingerbread, and neither does Chrome).