The unit is unable to act, though it can still move. Remove with Esuna.
Description (The War of the Lions)
Disable, also known as Don't Act on the PS version, is a status in Final Fantasy Tactics that makes a unit unable to act, evade, or use reaction abilities, including Shirahadori and Reflexes. At the end of an AT, a unit with Disable will have their CT decremented as if they had acted. Disable lasts for 24 ticks. Its counterpart is Immobilize, which prevents movement but not taking action.
DigiCube Guide Book (DigiCube) - Character Card Books (DigiCube) - Daizen (Famitsu) - Kōshiki Kōryakuhon (V Jump) - The Official Strategy Guide (Prima)
WotL books
Official Complete Guide (Square Enix) - Perfect Guide (Famitsu) - Tactics for Beginners (V Jump) - Official Strategy Guide (BradyGames)