An item to be held by a Pokémon. The holder gets a share of a battle's Exp. Points without battling.
When a Pokémon in the party holds an Exp. Share, they receive half the experience gained from battles. The remainder of the experience is divided between the battle's participants as usual.
If multiple Pokémon in the party are holding Exp. Shares, half the experience gained is split evenly between them while the other half is split between the battle's participants.