What is markup and why is it used on the web?
Markup is a way to add instructions to text so software can identify its structure or presentation. A heading, paragraph or link does not have to be guessed: markup makes its role explicit. HTML is the best-known example on the web.
How markup works
Markup separates content from structure. You write the content and add tags or symbols to identify what each part does. A browser or another program reads those marks and renders or processes the document.
HTML: the foundation of web pages
HTML (HyperText Markup Language) uses tags written between angle brackets. For example, <h1> marks a main heading, <p> marks a paragraph and <a> marks a link. Browsers interpret HTML to build the page you see.
Markdown: readable markup
Markdown uses lightweight symbols: # introduces a heading, **text** marks bold text and - item starts a list. It is common in README files, forums and note-taking apps because the source remains readable before conversion. A Markdown processor can turn it into HTML.
XML: structured information
XML (Extensible Markup Language) lets authors define tags to describe structured data. It appears in some APIs, RSS feeds, configuration files and document formats. Its purpose is to organize information so software can exchange or process it; it does not, by itself, specify how a page should look.
Markup is not the same as encoding
Markup describes the role or structure of content. Encoding changes how data is represented. Base64, for example, represents bytes with a limited set of characters; it does not label headings, paragraphs or links. The two ideas can be used together, but they solve different problems.
Try the concepts and keep learning
When you encounter a document format, check which language reads its markup and what that software does with it. HTML structures web pages, Markdown is often converted to HTML, and XML organizes data. For HTML reference material, MDN is a practical starting point.
References
These primary references document HTML, Markdown syntax and XML. The examples above are introductory; individual applications may support different features.
Frequently asked questions
Is Markdown a replacement for HTML?
No. Markdown is a simpler authoring format that many tools convert to HTML. The result and supported syntax depend on the processor.
Is Base64 a markup language?
No. Base64 encodes bytes as text characters; it does not describe a document structure.
Does XML control how information looks?
XML primarily organizes structured data. A separate application or stylesheet can determine how that data is presented.
A practical distinction
When markup and encoding are confused, it becomes harder to choose the right tool. Ask whether you need to describe the parts of a document or represent data in a transport-friendly form; that usually points to the right concept.