A game mechanic introduced in Pokémon Sword and Shield. Gigantamaxing increases a Pokémon's size and strength even more than regular dynamaxing, but unlike dynamaxing, their appearance changes significantly, as well.
An individual Pokémon needs to have a Gigantamax Factor to be able to Gigantamax. Giving the Max Soup to a compatible species will add or remove the Gigantamax Factor to it.
See Gigantamax (other) for Gigantamax forms created by fans.