What is a sport?

When watching equestrian (show jumping & horseracing), I used to wonder how such events got into the Olympics. I used to be of the belief that sports are events where you'd have to do an amount of running & sweating but it turns out that my concept of sport is biased. 

My preferred sports haven't changed but I'll now have to classify motorsport racing, equestrian, diving & maybe even board games as sports while rodeo & freestyle football are left out in the cold in the Olympics.