CP

CP, or Combat Power, is a measure of a Pokémon's power.

Higher CP values mean the Pokémon will be stronger and will hit harder.

When capturing Pokémon, CP is either directly displayed, or three questions marks may show (???). CP and the difficulty of catching a Pokémon is not always correlated, as it is possible for a low CP Pokémon to have a yellow ring when capturing.

The higher the level a trainer is, the higher the CP of a Pokémon can be. Wild Pokémon caught will also have higher CP as the trainer levels up.

This Reddit post shows a chart of how much CP is gained with each Power Up for all Pokémon.