Flinch is a single turn condition that can be inflicted upon a Pokémon. When a Pokémon flinches, it can not make it's move as it normally would be able to. Some items, such as the King's Rock, give the Pokémon a chance of causing the foe to flinch upon inflicting damage. A Pokémon that takes it's turn last cannot make another flinch because the condition will not be carried over to the next turn.
Moves that can cause flinching
Focus Punch (Self-induced flinching)