Pressure is an ability introduced in Generation III. So far, 5 Pokémon have this ability, none of which are available.
When a Pokémon with Pressure is targeted by a foe's move, one additional PP is deducted upon execution. If the move of a Pokémon targets several foes with Pressure, one additional PP will be deducted for each one.
Outside of battle
Pokémon with Pressure