Database migration
Also called: Schema migration
A step that changes an existing database from one schema version to the next without losing its data.
Definition
Installed apps keep their database across updates, so every schema change (a new column, a renamed table) needs a migration from the old version to the new one. Room supports auto-migrations for simple changes and hand-written SQL migrations for the rest; backends use tools like Flyway. Migrations are tested from old versions, because users skip updates.
In practice
Version 3 of a notes app adds a color column; the migration runs ALTER TABLE notes ADD COLUMN color INTEGER NOT NULL DEFAULT 0.