First of all, we have to understand the difference between the terms "Front-end / Back-end" and "Client side/Server-side" . "Back-end" usually refers to systems which are not directly exposed to the user (database servers, middleware and so on), while "front-end" usually refers to the application (in the case of the Web, this normally means static and dynamic web pages) directly accessed by the client. The interviewer started pointing out saying PHP (which is a language mentioned in my resume) is a "back-end" language. I didn't want to argue with him there, but I hope you are reading this answer. PHP is neither a "front-end" nor a "back-end" language, it can be both. But It is a "Server-side" language. Let me explain you why. You might create a webpage using PHP or even JavaScript or react. Imagine you are requesting something from a server. After you send a request, you don't care about anything what's happening within the server, you only care about what response you are getting. This "abstracted" part is called "back-end". The server could be using PHP or node or whatever for that matter. However, in your web application, the client (the user's browser), accesses web pages which are stored or dynamically generated "server-side" by "front-end" technologies. Those front-end components may, in turn, pull data or other information from "back-end" components. So a web application written in PHP would be "front-end" but "server-side". So, next time you ask anyone if about server-side languages, be specific that you are referring to "Server-side" languages, not "back-end". They both are completely different.