What is a Backend?

What you see on screen is only the storefront; the backend is the application's warehouse, accounting department and logistics — the part running on the server: it receives requests, applies business rules, reads and writes the database, talks to the tax platform, the couriers and the payment processor. When you press “Place order”, the button is frontend; checking stock, computing the discounted price, issuing the invoice and sending the confirmation email are backend. The distinction turns concrete in vendor quotes: a “brochure website” means minimal backend, cheap; anything involving user accounts, orders, stock or integrations means serious backend work — that's where the money actually goes and where the differences between seemingly identical offers hide. The backend also decides solidity: data security, speed under heavy traffic and the correctness of calculations are engine problems, not storefront problems.