Markup can be converted programmatically for display into, for example, HTML, PDF or Rich Text Format.
A markup language is a text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts.[1] Markup can control the display of a document or enrich its content to facilitate automated processing.
From Markup in MDN 
A markup language is one that is designed for defining and presenting text. HTML (HyperText Markup Language), is an example of a markup language.
Within a text file such as an HTML file, elements are marked up using tags which explain the purpose of that part of the content.
**Types of markup language**
Presentational Markup:
Used by traditional word processing system with WYSIWYG (what you see it is what you get); this is hidden from human authors, users and editors.
Procedural Markup:
Combined with text to provide instructions on text processing to programs. This text is visibly manipulated by the author.
Descriptive Markup:
Labels sections of documents as to how the program should handle them. For example, the HTML <td> defines a cell in a HTML table.
See also
Related glossary terms:
HTML
XHTML
XML
SVG
https://en.m.wikipedia.org/wiki/Markup_language
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