Fortnite Online Friends?

Hi, I have a question about the Fortnite lobby. I often read "ONLINE" in my friends list but what does that mean? Because if the person is playing or in the lobby is that then displayed.

I'm new to the game, just sit down with it. But so far I have not received an answer.

Hey it means that your friends have their epic games launcher open or started their PC. But fornite is a bad game