Software splits into two halves. The front end is everything that happens in front of the user: the layout, the buttons, the text, the animations, the forms. If you can see it or click it, it is front end. Everything behind the curtain (databases, logic, payments) is the back end.
A "front-end developer" builds interfaces. The front end of a website is typically built with HTML, CSS and JavaScript, three languages the browser understands.
Why you keep hearing it
Because AI tools have become startlingly good at front-end work. Generating a decent-looking page from a text description is now table stakes for tools like Lovable and v0. When someone shows off an app they "built with AI in an afternoon", what you are usually seeing first is a generated front end.
What it means for you
For marketers, the front end is where brand lives in a product: the look, the words, the feel. Knowing the term helps you talk to developers precisely. "The front end feels dated" and "the back end is slow" are different problems, sent to different people, and using the right one saves everyone a meeting.