Why would one have to use a catheter daily?

I have been seeing a lot of tele commercials lately regarding catheter ordering/sales for those who use them daily (mostly women depicted in the commercials). I sincerely (and empathetically) just wanted to know why these poor women unfortunately would have to use catheters daily, and what exactly are they? I had always thought it was some kind of urinary device? I was just wondering, as I see these on the tele all the time.