The code of the project names the databases the way production does : shop. On a developer machine the same database may be shop_dev, or two developers may share one server with shop_alice and shop_bob. Masking maps one to the other, for one account, so nobody edits a database name before a pull request.
Where
Profile → User info → masked databases : instance, database name, masked database name.
Scope
The account of the developer only. Git, schemas, settings and code keep the name of the project.
Effect
Every API, hook, migration and query of the account runs on the masked name : the name in the URL and in the code stays the one of the project.
Instance
Database name (in the code)
Masked database name (on this server)
mysql8
shop
shop_alice
Add one row per database whose name differs. Names not listed are used as they are.
Table meta, migrations, plain queries which name the database in the API also go through the mapping ; SQL text you write yourself does not.