Js refers to JavaScript, a high-level programming language primarily used for creating interactive and dynamic content on websites. It allows developers to implement complex features such as animations, form validations, and real-time updates without needing to refresh the page. JavaScript is an essential part of web development, often used alongside HTML and CSS. Originally developed by Netscape in the mid-1990s, JavaScript has evolved significantly and is now supported by all major web browsers. It is also used in server-side development through environments like Node.js, enabling developers to build full-stack applications. Its versatility and widespread adoption make it a fundamental skill for web developers.