JavaScript is a programming language first released in December 1995 by Brendan Eichof Netscape. If HTML handles a website's 'structure' and CSS manages its 'design,' JavaScript controls its 'behavior' to make web pages dynamic. It is a core technology that brings the web to life, responding to user clicks, validating input values, and creating animation effects. Today, it is used not only in web browsers but also in various environments such as servers.