Often the frontend is called the place where the user experience takes place. The counter part of the frontend is, you guessed it, the backend. The backend handles the data that is produced or prepared for the frontend. A frontend can be a web application, a dekstop application, a smartphone app, a smart watch app or even a ticket wending machine. In short, every user interface that has some what a backend behind it, is called a frontend. Nowadays most popular frontends are the ones created for the web, let's call them web frontends, because they are run in the web browser.
In the early days web browsers have been used to deliver information only. You could open a web page for a restaurant, get some information about the menu, opening hours or location, close it and done. Today, we deliver in addition to that a completely new and different experience. We want the users to stay on our page. A web browser is a great platform for creating more value for the user. Just imagine the amount of devices that have web browsers pre installed: Notebooks, smartphones, tablets, yet even game consoles have web browsers installed. It's crazy.
Web browsers are the portal to the internet for everybody and thus to that experience. We as frontend developers take a great role in creating and enhancing that experience. We can create something that is immediately available for billions of devices. We are the ones that are actively participating in producing that experience. We are at the front door.
A bad frontend would make the users unconfortable using your solution and they would probably not like to come back. Imagine a good frontend to be a store or a restaurant where the user actually wants to visit often. A good frontend makes the user happy, leaves a positive experience and ensures the user comes back again.
So my dear friend, create something awesome where the user wants to come back and stay at your place. It will not be an easy journey, but it will sure be worth it at the end!