Back end

Also called: backend, back-end, server side, business logic

The part of an app that runs out of sight on a server. It saves information, checks who is allowed to do what and does the work the front end asks for. Any app that has accounts or saves information needs one, including apps made with no-code or AI tools.

For example: You tap 'Place order'. The front end shows the button. The back end checks the payment, saves the order to the database and sends the receipt.