Other forms: lesser
If something is less, there's not as much of it as there was before, or compared to something else. For example, your cranky uncle might complain that there's less common sense in the world than there used to be.
If you have less money than you did last month, there's not as much of it, and if you're less interested in horror movies than you used to be, your enthusiasm has decreased. Many people aren't sure when to use less and when fewer is correct. In general, fewer is for things you can count (like chocolate chips), and less is for things you can't count (like love or water or salad).