JavaScript
JavaScript is a programming language used to give functionality or behavior to a web page. For example, when toggling the visibility of a dropdown menu, often JavaScript is used. It runs in the browser and works by manipulating the HTML document.
It is the most commonly used programming language on earth. JavaScript is not limited to use in the front-end, but can also be used in the back-end.
The standard that describes JavaScript is called ECMAScript. The latest version is called ECMAScript 2015 (or ES2015), which is sometimes referred to as ECMAScript 6 (or ES6).