This article is from the Juggling FAQ, by Juggling Information Service firstname.lastname@example.org with numerous contributions by others.
They are site swaps.
Site swaps are strings of numbers, each number refers to how high a
throw is in relation to others in the pattern. Even numbers are
thrown to the same hand, odd numbers are thrown across to the other
hand. The numbers then, tell the right hand what to do, then the
left, the the right, etc. For example:
3 The three object cascade
4 The 4 object fountain pattern (alternating) 5 The 5 object cascade pattern 5 1 The 3 object non-synchronous shower (1 is a quick pass from hand to hand)