From Bulbapedia, the community-driven Pokémon encyclopedia.
Jamming is a term used in Pokémon Contests and is a feature only in Generation III; it refers to when an appeal can lower the appeal points of the other Pokémon in the Contest by the number of black hearts represented above the number of appeal points the move makes.
If not executed correctly it only says that the move messed up, and it still gains appeal points and any other extra, for example, if a move that affects all Pokémon after the user is played last. On the other hand, if the move backfires on the user, it causes them to lose appeal points.
Moves which can jam
- Out of all the types, the Normal-type has the most moves that can jam, with 36.
- Out of both damage categories, Physical moves have the most moves that can jam, with 49.
- Out of all the Contest categories, Smart moves have the most moves that can jam, with 34.
- Out of all of the moves that can jam, the fewest amount of moves removing appeal points is two points, with only five moves.