More specifically, it is an idea and a call to arms against those who label their sites "best viewed in browser x", and through that, it is a campagin against the proprietary extensions to HTML that many browsers have introduced. This campaign goes almost hand-in-hand with web standards and aims to prevent HTML atrocity that has been brought on by these propreitary extensions (All this helps lessen the power of HTML satan, of course.) One of the possible solutions to the problem of browsers and HTML is to use Strict HTML and XHTML Strict more.