It cannot be knocked out with one hit.
Sturdy is an ability introduced in Generation 3. So far, 8 Pokémon have this ability.
As long as the Pokémon has full health, it will not be taken out in one hit, and will have one HP remaining. It is also immune to one-hit KO moves.
Outside of battle
Sturdy has no effect outside of battle.
Pokémon with Sturdy