The Armor Break is a mechanic introduced in the Street Fighter IV series.
Each character in the games has at least one attack (such as Guile's Flash Kick or M. Bison's Psycho Crusher) with which they can bypass a character's Super Armor; each character will also have an Armor Breaking Ultra Combo as well. When a character with Super Armor is struck by an armor-breaking attack, there is a sound and a visual effect of glass shattering, while the attack itself proceeds as normal.
Breaking an opponent's armor does more damage and stun than the attack would normally deal and also causes knockback. This is not the same as depleting the opponent's armor (by hitting them with a non armor-breaking attack) as it lacks the damage and stun bonus of an armor break (the same is true for Throws and Command Grabs). Moves with armor breaking properties are also immune to Counter Attacks.