Backend or Back-end is jargon thrown around by web developers as an umbrella term for all of the parts of a website that are behind the scenes, in contrast to the parts that you can interact with in a browser.
The back end is the transmission, engine and exhaust to the front end’s dashboard, steering wheel and pedals. The backend is what’s going on in the background of a website. It knows how to communicate with databases or other websites and send information to the “front end” for display.
When visiting a website in a browser, it’s the systems and code that run backstage in order to accomplish all of a website’s goals and make it really work. The backend can send emails, sms and smart phone notifications, it can update databases and mark “one more person viewed this video”. It manages logging in and knows that you’re you and someone else shouldn’t have access to your bank account info.
Within each programming language’s ecosystem, there are libraries and tools called “frameworks’ to help build website backends. Some popular examples are Express, Rails, Django, Spring, .NETMVC and Laravel. Each of these frameworks know how to communicate with browsers using HTTP, the HyperText Transfer Protocol and know how to take actions when websites are visited.