From Bulbapedia, the community-driven Pokémon encyclopedia.
A Lass (Japanese ミニスカート Mini Skirt) is a type of Pokémon trainer that first debuted in the Generation I games. They are depicted as average young girls in cute clothing.
They use a variety of Pokémon.
Blue was based on the early character designs of the Lass characters.
The Lass character wears a private school uniform.
In the TCG
In the TCG, the Lass character has their own card in the Base Set.