XML stands for eXtensible Markup Language. It is extensible, because it does not use a predefined set of tags for identifying structural components. Instead, it provides a mechanism for defining such sets of tags. The main purpose of the language is to share data. Unlike HTML, in XML there is no predefined set of tags and tags specify meaning, rather than the presentation.
XML syntax refers to the rules that determine how an XML application can be written. XML syntax is very straight forward, and this makes XML very easy to learn.
In Computer Language, eXtensible Markup Language(XML) is that which defines a set or block of rules which are later used for encoding documents in such a format which is both machine and human readable.
XML was replaced by JSON as the main language for transferring data but XML is still widely used to create user interfaces for Android, JavaFX and general GUI design due to its expressive quality. The following example is a view created with a framework called SAPUI5 that uses XML:
As you can see, XML is quite similar to HTML, but the difference lies in the functionality.
There is a main thing between XML and HTML which makes them different from each other. It is that XML was designed to carry a particular information and focuses on that informaion only. And HTML focuses on displaying that particular Information like design and all these stuff regarding the information.