A crush is defined informally in the dictionary as:
I think that there are a variety of crushes that one might have over the course of their lives, but they all kind of boil down to being a school girl crush. One that makes you feel juvenile and powerless under the one that you adore. One that makes you feel silly and hopeful for all the wrong reasons.
These are the kind of crushes that create pipe dreams that, never fulfilled, will be mourned over for weeks if not months. School girl crushes are wishes never granted that consistantly give the promise of a broken heart.