An ECMAScript engine is a software platform that can run code written in ECMAScript, a programming language more commonly known as JavaScript.
More formally, an ECMAScript engine is, at least in part, a "conforming implementation" of the ECMAScript programming language specified by the ECMA-262 international standard.
Many implementations of ECMAScript engines are available, which differ based on the platforms they are intended to support, their level of conformance, and other implementation-specific characteristics. This article attempts to provide a relatively comprehensive list of engines that execute ECMAScript code.
The uses of the listed engines vary widely; some of these are engines intended for browsers that can run ECMAScript code on websites that include ECMAScript, like V8 (used in both Google Chrome and Node.js) and SpiderMonkey; some are intended for specific platforms (like Tamarin, Espruino, Rhino, Nashorn, and GraalJS). 
Browser engines.
Web browsers that support JavaScript embed JavaScript engines in order to support JavaScript-enabled web pages. Different browsers use different engines, although there are now multiple browsers based on Chromium which use V8 as their JavaScript engine.
Obsolete browsers and engines.
Some engines either power JavaScript in obsolete browsers (like Internet Explorer), or have subsequently been replaced (as the engine has in Opera, with its move to Chromium).
References.
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