Originally posted by meehs
It's the angle of incidence between the top tube (if it's horizontal, if not, use an imaginary horizontal top tube) and the seat tube and the head tube respectively. It's best just to look them up rather than try to measure them since it's not real easy to measure if you don't know what you're doing. Generally the steeper the angles the quicker the bike handles and the slacker the angles the more stable the bike is. Road bikes have steeper angles than mountain bikes.