HTML (Hypertext Markup Language) is the standard language used to create and design documents on the World Wide Web. It provides the structure and content of web pages by using various tags and elements to define different parts of a page, such as headings, paragraphs, images, links, and more. CSS (Cascading Style Sheets) is a style sheet language used to control the presentation and layout of HTML documents. It allows web developers to define the visual appearance of web pages, including elements like colors, fonts, spacing, borders, and positioning. CSS enables the separation of content from design, making it easier to maintain and update the look and feel of a website across multiple pages.