Web technologies related to the interface between web servers and their clients. This information includes markup languages, programming interfaces and languages, and standards for document identification and display.

HTML

XHTML

SGML

MathML

XML

GML

are a few Markup Languages to name

A markup language adds codes to content that is interpreted to have specific meanings to different programs. There are many different types of markup languages. The markup language used most of the time on the Web is HTML. Hyper Text Markup Language (HTML) tells a browser how to format and display content. For example These Words tells the browser to display the characters between the tags as bold.

Markup languages are used to store data, so no--they are not used only on the client side.

XML allows programmers to define markup languages for use in their own programs. Popular XML based language files include things like Microsoft's .docx file format.

HTML can be said as Hyper Text Markup Language. It is a language which works as Markup tags.