HTML
First developed by Tim Berners-Lee in 1990, HTML is short for Hypertext Markup Language. HTML is used to create electronic documents (called pages) that are displayed on the World Wide Web. Each page contains a series of connections to other pages called hyperlinks. Every web page you see on the Internet is written using one version of HTML code or another.
CSS
Short for cascading style sheets, CSS is a language used to describe reusable styles for presenting documents written in a markup language. Its concept was originated by Håkon Wium Lie in 1994. In December 1996, CSS was made a specification by the W3C and today allows web developers to alter the layout and appearance of their web pages. For example, CSS may be used to change the font used in certain HTML element, and its size and color.
JS
JavaScript is a text-based programming language used both on the client-side and server-side that allows you to make web pages interactive. Where HTML and CSS are languages that give structure and style to web pages, JavaScript gives web pages interactive elements that engage a user. Common examples of JavaScript that you might use every day include the search box on Amazon, a news recap video embedded on The New York Times, or refreshing your Twitter feed.