An adrenaline rush. Feeling the horse pushing off of the ground, the feeling of extreme power and freedom. Feeling like you are flying, leaving your worries behind you.
Horse jumping is the best, free-est, most powerful adrenaline rush you will ever have.
A hardo is a person who tries extremely hard at everything. Most times a hardo will try very hard at things that do not require excessive effort. For example, sports practices, gym class, etc.
Wow did you see Jack at practice today? What a hardo!