ECMAScript

ECMAScript is the standardized version of JavaScript by the organization ECMA (originally European Computer Manufacturers' Association, preferring now to go by the de-acronymized version of its name, Ecma, which looks like a skin disease). It was created in the wake of not-quite-compatible implementations of the scripting language during the late '90s browser wars; Netscape had JavaScript, while Microsoft had its own ripoff, JScript. ECMAScript codified an interoperable version of the language. This standardization has succeeded to the extent that modern browsers are now able to run very complex things, like JSMESS, across different browsers and platforms.

Purists make a big deal about the distinctions between the various *scripts; "Don't call it 'JavaScript' when that particular chunk of code is really 'JScript' or 'ECMAScript'!" The public, and even most tech types, blithely ignores it and calls the whole messy cluster of scripting languages "JavaScript" (that emulation project is JSMESS, not ECMASMESS), and stores it in .js files and tags it with the  MIME type, despite the existence of other "official" extensions and MIME types for different script variations such as ECMAScript. And the scripts generally run fairly well on the newest browsers no matter what the browser makers happen to call the scripting language within their own platform.

ECMAScript is standardized as ECMA-262, which has had a number of revisions over the years. A version is also standardized as ISO/IEC 16262, which can be found in a "free" version (downloadable from ISO at no charge, but which all sorts of licensing conditions you have to click through, and in a locked-up PDF file) as well as a paywalled version (just why somebody would pay for a file that's available free is unlcear). The ECMA versions, on the other hand, are out on the web for free.

Standards

 * ECMA-262 spec, 3rd edition, 1999
 * ECMA-262 spec, final 3rd edition, 2000
 * ECMA-262 spec, 5th edition, 2009
 * ECMA-262 spec, version 5.1, 2011
 * ISO/IEC 16262 2011

Other links

 * Official site
 * Wikipedia article