My understanding from small MVC applications is that you have the front end, which deals with HTML, JS, jQuery, etc, and you have the back end, which consists of your controllers and models.

However, when I talk to developers from large companies, they often mention having a frontend tier and a backend tier. So sometimes, I might hear that they have a frontend with C# and a backend with Java. Why would any company want a backend and frontend in different languages? Does this help the large website scale better?

When people say that their frontend is built in C#, does this mean that they are using a framework for the frontend (like .NET) and an additional framework on the backend (such as Spring)? Or does it mean something entirely different?