The backend (or “server-side”) is the portion of the website you don’t see. It’s responsible for storing and organizing data, and ensuring everything on the client-side actually works. The backend communicates with the front-end, sending and receiving information to be displayed as a web page. Whenever you fill out a contact form, type in a web address, or make a purchase (any user interaction on the client-side), your browser sends a request to the server-side, which returns information in the form of frontend code that the browser can interpret and display.
The parts of your web application which are intended to be used directly by the the user’s browser. The frontend of a website is what you see and interact with on your browser. Also referred to as “client-side”, it includes everything the user experiences directly: from text and colors to buttons, images, and navigation menus.
The backend and frontend both work together to serve a single goal. It’s pretty helpful to keep it in mind at all times.