The Pokémon Pokopia Expansion Pass includes three waves of content.
Nintendo describes the paid downloadable content as adding new towns, new Pokémon to befriend, and new features for players to enjoy. Presenting the pass in waves means its additions are scheduled or delivered in separate content releases rather than as one single update.
The number three refers to the structure of the Expansion Pass, not the number of Pokémon, towns, or features added by the entire package. Those categories can contain multiple individual additions and should not be treated as a three-item total.
The pass is separate from the base game's launch content. Players can experience Pokopia's main building and habitat systems without treating the three-wave Expansion Pass as part of the game's original release package.