A crush or infatuation an individual holds upon a male child.
Julie had a serious boycrush on Christopher Knight when he was playing Peter Brady on tv.
A boycrush is a term for a guy that holds non-sexual affection for another guy, looks up to another man and idolizes him and wants to be like him, etc.
The term has nothing to do with homosexuality in and of itself, although it might be on the borderline sometimes. For example if a straight guy really enjoys spending time with his male best friend and has lots of sentimental feelings for him that are perhaps stereotypically 'Un-American', he is said to have a 'boycrush.'
Because of our society, it's probably quite common for somebody to hide their innocent boycrushes.
"Jeff has such a boycrush on John, it's kind of cute."
"He talks about his favorite sports hero so much, you would think he had a boycrush."
"The male cast members of 'Friends' sure had lots of boycrushes on each other."