what is xml used for?

Hello
I hope you all are well!
It is two months that I have learned xml and I rarely used it.
The reason that I have rarely used it,is that I really don't know exactly 
what it is used for.
I want to have overview about the usage of xml.
I would be happy if any one of my friends help me in this case and tell me 
some of its usages.
By the way I'm a computer engineering students and I can't make head or 
tails of commercial activities if you want to tell me some usages of xml 
in them.
thank you very much
AmirHossein GholamiPour