HTML (HyperText Markup Language) is the standard markup language for documents designed to be displayed in a web browser. It defines the structure and content of a web page.
CSS (Cascading Style Sheets) is a stylesheet language used to describe the presentation of a document written in HTML. CSS describes how elements should be rendered on screen, paper, or in other media.
JavaScript is a scripting language that enables you to create dynamically updating content, control multimedia, animate images, and much more. It is the third layer of the standard web technologies layer cake.