It’s not a file name. It’s shell syntax. Specifically, https://en.wikipedia.org/wiki/Job_control_(Unix)

That’s a pretty terrible article on the subject, but I don’t have a better one at hand. You could read some shell scripting tutorial or manual or maybe a beginners guide to Unix. A decent one should explain job control well.

But basically, in a script or command line, an ampersand ends a command and runs it in the background without waiting for it to finish before running the next command. A semicolon works the same but waits on the foreground.