What is getting a residency in Vegas mean?

I heard Joe Rogan's podcast recently and he mentioned about how "sad" he felt for a comedian because they were doing a residency in Vegas. Joe Rogan said something along the lines that only 4-5 people showed up for the show but you still had to do your act etc. He made it sound like it was a pretty bad scenario.

When I google Las Vegas residency I see big names like Lady Gaga, Celine Dion etc and it seems like its extremely lucrative and shows are almost sold out.

Is it different for comedy?