What are client side languages

What are client side languages

html ,css  are client side languages  and the question here arises how we would know that this is client side language or server side language ,
the difference is great as where post and get method is used there we can see the example of php
which is server side language .
and one more difference is that when we want to call a object etc. we use server side language and today programming is object oriented programming.