migration

Think of renovating a kitchen while keeping all your dishes. A migration is a change plan for your database that preserves what you already have.

It matters because features evolve. You add a table, a named collection of rows, or a column, a named field in a table, and you want the same steps in every environment, from your laptop to production.

In practice a migration is a small file that says what to change and often how to undo it. You commit these files to GitHub so teammates and servers run the same changes in order.