Most Pokémon evolve into other forms when certain conditions are met, such as when they reach a certain level—levels range from 1 to 100—or have a certain item used on them. They can learn up to four moves, including attacking moves, healing moves, and moves that inflict status conditions on the opponent. They have six stats that affect battle performance: maximum HP (hit points), Attack, Defense, Special Attack, Special Defense, and Speed. Attack and Special Attack are distinguished from Defense and Special Defense by the types of moves being considered: generally, moves involving physical exertion are physical, while moves involving supernatural or elemental powers are special. Moves are classed as one of seventeen types, (Normal, Water, Grass, Fire, Electric, Ghost, Bug, Fighting, Ice, Steel, Rock, Poison, Psychic, Dark, Dragon, Ground, and Flying); Pokémon can have one or two types. Generally, most of a Pokémon's moves correspond to its typing. A Pokémon's type makes it vulnerable or resistant to others; for example, Fire-type Pokémon are weak to Water-type moves, while Grass-type moves do little damage to them and Electric-type moves do normal damage.