HTML (HyperText Markup Language) is the standard markup language for creating web pages. It describes the structure of a web page semantically and originally included cues for the appearance of the document.
CSS (Cascading Style Sheets) is a style sheet language used for describing the presentation of a document written in HTML or XML. CSS describes how elements should be rendered on screen, on paper, in speech, or on other media.
JavaScript is a high-level, interpreted programming language that conforms to the ECMAScript specification. It is a language that is also characterized as dynamic, weakly typed, prototype-based and multi-paradigm.
Responsive web design is an approach to web design that makes web pages render well on a variety of devices and window or screen sizes. It ensures that users have a good viewing experience no matter what device they're using.
Web APIs are application programming interfaces for the Web. They extend the functionality of the browser and enable you to build complex web applications. Browser APIs are built into your web browser and can expose data from the browser and surrounding computer environment.