wave height is the avg height of the waves for a certain period of time . .. .
swell . . . every couple waves, like 8 or so, there is what's called a dominate wave that is significantly higher than the rest. usually this wave is about half foot higher or so than the rest. that's what they base the swells on . . . best way to think about it is like wind speed and wind gusts . . same thing but in waves