Library / Data & backend / Backend
No. 042·noun·also called back end, server, server side

Backend

The behind-the-scenes part of an app that stores data, enforces rules, and does the work you don't see.

SPECIMEN · DIAGRAM · FLOW
PersonFrontendasks
AppBackendchecks rules
DataDatabase
ServiceEmail service
requestread/writesend
Definition

What it is

The backend runs on servers, not on the person's device. It saves and fetches data, checks permissions, sends emails, charges cards, and talks to other services. It's the restaurant's kitchen.

Anything that must be trusted belongs here: "only the owner can edit this", "an order can't be refunded twice", "this API key stays secret". The frontend just asks; the backend decides.

When you describe a feature, separating what people see (frontend) from what must be true (backend) helps a coding agent put each piece in the right place.

Say it like a builder

How to ask for it

Vague

“Only managers should be able to approve expenses, so hide the button for everyone else.”

Precise

“Only users with the manager role can approve expenses. Enforce this in the backend (reject the approval for anyone else), and also hide the Approve button in the frontend for non-managers.”

Why it works

Hiding a button alone is not security; naming the backend makes sure the rule is actually enforced.

In the wild

You've seen this in

  • GGmail sorting spam before you see it
  • SStripe charging a card
  • SSlack sending a push notification
Usage note

Often confused with

FrontendThe frontend shows things on your device; the backend stores data and enforces rules on a server.DatabaseThe database is where data sits; the backend is the logic that reads and writes it.