As a WPF developer, I was confused when I discovered that I'm not considered front-end because my platform isn't web, even though I clearly deal with user interaction and the front end of an application.
One thought I had was that desktop applications don't have a separation between the front and back ends (the UI and domain, respectively) like the web does. However many applications do have this distinction, especially in the enterprise. Most of the desktop applications I've developed professionally were merely desktop clients for data served up and received by web APIs. In this sense, the client is very much the front end.
In this answer, the writer states that "front-end" must run in a browser whereas "client-side" could potentially include desktop applications.
So... why does "front-end" only pertain to web development?
#include <libpq-fe.h>
when working with PostreSQL client lib. Etc. Anyway, you get the idea.