HTML stands for HyperText Markup Language. It is the standard markup language used to create and structure content on the web. HTML elements are the building blocks of web pages and are represented by tags such as <h1>, <p>, and <div>.
CSS stands for Cascading Style Sheets. It is a stylesheet language used to describe the presentation of a document written in HTML. CSS controls layout, colors, fonts, spacing, and overall visual appearance of web pages.
JavaScript is a versatile programming language primarily used to create interactive and dynamic content on websites. It runs in the browser and can manipulate the DOM, handle events, communicate with servers, and much more. It is one of the core technologies of the World Wide Web alongside HTML and CSS.
Responsive design is an approach to web design that ensures web pages render well on a variety of devices and screen sizes. It uses flexible grids, flexible images, and CSS media queries to adapt the layout to the viewing environment.