This document explains the basic ideas behind databases in the PlanetScaleDB context.
A PlanetScaleDB database is like a MySQL database that can scale horizontally using sharding. Each database runs on a cluster. A database deploys to one or more of the cloud providers and regions which that cluster supports.
You can assign resources to each database at the time of database creation. You can also choose to create multiple instances of particular databases to improve availability and serve more read traffic.