Frontend / Backend
The two halves of a digital system: frontend is what a user sees, backend is the server-side logic and data behind it — adjacent professional vocabulary.
In practice
The frontend is the part of a website or app that runs in front of the user: screens, buttons, animations. The backend runs on servers, storing data, checking passwords and doing calculations. Designers work mostly with the frontend but need to understand the backend's limits. A search screen may look simple, yet whether it can show results instantly as someone types depends on how fast the backend can answer.
Often confused with User Interface (UI)
UI is the designed layer of controls a person uses; the frontend is the code that builds and runs that layer in a browser or app.
Try this
Pick an app you use and list which of its features need data from a server and which still work offline.