Derek updated his blog on Capcom-Unity with a really good explanation of the frame system in Street Fighter.When your opponent blocks an attack, they become stuck in the blocking animation for a short period of time. During this time, they are unable to move, attack, jump, or do anything else. This is called block-stun.
When you hit an opponent in the face with a move, pretty much the same thing happens. While the opponent is recovering from being hit, they cannot move, attack, jump, or even block! This is called hit-stun.
This article is part of a Street Fighter 101 training course which has some great stuff in there, here's a link to the index page.
