A non legendery Pokemon with a base stat total of 600.
>Pseudo-legendary Pokémon (Japanese: 擬似伝説 Pseudo-legendary) is a fan term commonly used to refer to any Pokémon that has a three-stage evolution line, 1,250,000 experience at level 100, and a base stat total of exactly 600. The term originates from the prefix pseudo-, which means "false". Pseudo-legendary Pokémon are often more powerful than other non-legendary Pokémon due to their high base stats.
Other variations of the definition also mention having two types or having at least one type immunity, or omit the need to have 1,250,000 experience at level 100.
Here is a list