Party

Party is a group of six Pokémon that a Trainer carries with them.

History
Teams are usually restricted to six, but a Pokémon or an egg that a trainer carries without a Poké Ball can still travel with them. After a Trainer catches more than six, they are typically sent to a respective region's professor or they shrink and are unable to be enlarged, if a Trainer is too far from a regional professor.

In Galar, however, there are not any party restrictions and people are allowed to use more than six Pokémon outside of battle. People are able to use their Rotom Phone to check what Pokémon they have at Professor Magnolia's Lab.

In Nanu's Paradise: chapter 9, Kukui upgraded and changed how many Pokémon people can carry, allowing people to carry more than six Pokémon, but they cannot be used in battle, as they will be blocked by a beam if they try to battle with them.