JavaScript (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, and is best known as the scripting language for Web pages, but it’s used in many non-browser environments as well. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.
Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/About_JavaScript
Alongside HTML and CSS, JavaScript is one of the three core technologies of World Wide Web content production.
Each of the many JavaScript engines represent a different implementation of JavaScript, all based on the ECMAScript specification, with some engines not supporting the spec fully, and with many engines supporting additional features beyond ECMA.
Source: https://en.wikipedia.org/wiki/JavaScript