Front End and Back End.

A restaurant is a good picture of it: the front end is the dining room with menu, tables and service. The back end is the kitchen with its stores, recipes and ordering system. Guests never see the kitchen, but they notice immediately when it does not work. On a website, the front end is everything that happens in the browser — HTML, CSS and JavaScript. The back end runs on the server: it receives form submissions, checks logins, calculates prices, stores data and sends emails.

Typical front-end technologies are HTML, CSS, JavaScript and frameworks such as React or Next.js. On the back end you find programming languages such as JavaScript (Node.js), PHP or Python, plus databases such as PostgreSQL or MySQL and APIs for connecting to other systems. Someone who masters both sides is called a full-stack developer. Modern frameworks blur the boundary: with Next.js, parts of the logic run on the server and parts in the browser, within the same project.

For clients the distinction matters above all when comparing quotes. A purely informational website has a lean back end — a CMS, or none at all if the content lives in the code. A booking system, a customer portal or a web app, by contrast, has an extensive back end with user management, permissions, database, notifications and reporting. The visible part can look similar in both cases; the effort behind it differs many times over.

Most problems arise at the interface between the two. A front end that only validates input in the browser is insecure, because any check in the browser can be bypassed — binding validation belongs in the back end. Conversely, the best back end is of little use if the front end loads slowly or is awkward to use on a phone. Good projects plan both sides together rather than handing them to separate teams that never talk to each other.