What is ECMAScript?
ECMA stands for - European Computer Manufacturer's Association. ECMAScript is a standard for a scripting language. It specifies the core features that a scripting language should provide and how those features should be implemented. Javascript was originally created at Netscape, and they wanted to standardize the language. So, they submitted the language to the European Computer Manufacturer’s Association (ECMA) for standardization. But, there were trademark issues with the name Javascript, and the standard became called ECMAScript, which is the name it holds today as well.
So you can use any scripting language that implements the ECMA standard as the web browsers support the ECMAScript interpretation when you are specifying (<script type="text/ecmascript">).
ECMAScript = ES:
ECMAScript is a Standard for a scripting languages.
Languages like Javascript are based on the ECMAScript standard.
ECMA Standard is based on several originating technologies, the most well known being JavaScript (Netscape) and JScript (Microsoft).
ECMA means European Computer Manufacturer’s Association
On the other side:
JavaScript = JS:
JavaScript is the most popular implementations of the ECMAScript Standard.
The core features of Javascript are based on the ECMAScript standard, but Javascript also has other additional features that are not in the ECMA specifications/standard.
ActionScript and JScript are another languages that implements the ECMAScript.
JavaScript was submitted to ECMA for standardization but due to trademark issues with the name Javascript the standard became called ECMAScript.
Every browser has a JavaScript interpreter.
For more details on this checkout my full answer here What is the difference between JavaScript and ECMAScript?
ECMAScript is a standard. JavaScript and ActionScript are well-known implementations of the ECMAScript standard.
http://en.wikipedia.org/wiki/ECMAScript
JavaScript is a subset of ECMAScript. JavaScript is basically ECMAScript at its core but builds upon it. Languages such as ActionScript, JavaScript, JScript all use ECMAScript as its core. As a comparison, AS/JS/JScript are 3 different cars, but they all use the same engine... each of their exteriors is different though, and there have been several modifications done to each to make it unique.
The history is, Brendan Eich created Mocha which became LiveScript, and later JavaScript. Netscape presented JavaScript to Ecma International, which develops standards and it was renamed to ECMA-262 aka ECMAScript.
It's important to note that Brendan Eich's "JavaScript" is not the same JavaScript that is a dialect of ECMAScript. He built the core language which was renamed to ECMAScript, which differs from the JavaScript which browser-vendors implement nowadays.
http://en.wikipedia.org/wiki/ECMAScript