Repels are items in the Pokémon series which keeps Wild Pokémon with a level lower than the Pokémon in the front of the party away. It must be used out of battle and the effect of a Repel wears off after walking a hundred steps.
There are also Super Repels that keep away Wild Pokémon for 200 steps and Max Repels that keep Wild Pokémon away for 250 steps.