Unlike plain XML, CAML contains specific groups of tags to both define and display (render) data.
Data definition elements define lists and sites in the same style as basic XML (but with a limited set of keywords).
For example, the following example loops through some data and generates an HTML drop down menu of choices: In general, almost all XML files in a SharePoint installation utilize CAML.
Here the CAML defines what elements exist on an instance of a site, and the display of these sub-elements, while the ASPX files define how to arrange and display those elements to form the site.
CAML can be used to perform the query based operations like filtering the data in lists and library