You can set the label to anything, but it's best to pick a label that makes it clear how you got the experience.

Is the opposing Pokémon a wild Pokémon?

Pokémon obtained via an international trade gain additional experience starting in Gen. 4.

If a Pokémon is gaining experience via the Exp. Share but did not participate in the fight, uncheck this box.

The number of unfainted Pokémon that also participated in this fight, not including this Pokémon. In most cases, this will be 0.

Is this Pokémon affected by an Exp. Share?

The number of Pokémon in the party, not including this Pokémon, that are holding an Exp. Share.

Is this Pokémon holding a Lucky Egg?

Does the Pokémon have an Affection of at least 2?