PP

From the Pokémon Wiki, a database for the Pokémon series that anyone can contribute to

PP is an abbreviation of Power Points. Power Points measure the number of times you can use a move. The higher PP, the more times you can use the move. They are essential for attacking, supporting, stalling, recovering, and defending. They are also significant for Trump Card, the Metronome item (based on consecutive usage of the same move), Fury Cutter, and some others.

Generally, Moves with a lower PP are better than a move with higher PP. This is not always true.