In the Pokémon games, the player can capture a Pokémon he/she likes to have in his/her team, but mostly the catch doesn't succeed as they hope it to be. Each Pokémon has a catch rate. It depends on the Pokémon, the Pokémon's HP, and the type of Poké Ball the player uses.
The lowest catch rate is 3, which belongs to the Beldum family and almost every legendary Pokémon in the game. A low catch rate means that the Pokémon is very hard to catch, often meaning the player must use over 20 Poké Balls or more. The highest catch rate is 255, which belongs to small Pokémon such as Caterpie or Pidgey, which can be easily caught with a Poké Ball without the need to damage them.
Depending on the amount of HP, current status ailment, level of the Pokémon, and/or the Poké Ball being used, the chances may raise or lower. Because of this, the player may sometimes have to use stronger Poké Balls or more of them to catch the desired Pokémon. If an attempt to catch a Pokémon fails too many times, the Pokémon may flee.