var is not a keyword according to this list.
it is a contextual keyword, so from the context, the compiler is able to decide which is your class and which is the contextual keyword, and no confusion arises.
a contextual keyword is:
used to provide a specific meaning in the code, but it is not a
reserved word in C#.
so as it’s not reserved you can use it.
As pointed out in the comments above there is a discussion of the differences as well as a list of the various keywords and contextual keywords added at each version of c# on Eric Lippert’s blog
It is interesting to note that since the set of keywords was decided upon in C#1.0 there have been no additions, so as to preserve backward compatibility.