It depends on what your goals are and what you expect to be studying in college.
In general I would expect to revisit pretty much anything you've done in high school (post the usual high school subjects of basic algebra, geometry, etc.) in college in greater depth. That was certainly the case for me except for a few algebra topics covered in pre-calc that I never saw again (I was a physics major and took mostly applied math classes in college).
Math is such a vast subject that you could choose many areas to get a very basic introduction to in a month (ie. basic abstract algebra/group theory, number theory, probability, etc.) It really depends on what interests you the most.
