To take a brief nap. Ever notice how cats tend to fall asleep, wake up shortly thereafter, and then doze off again? Catnaps are referred to as such due to their brief and sometimes random nature.
Person A: "Say, is Heather awake?"
Person B: "No, she said she was tired and wanted to take a quick catnap.
To steal or kidnap a pet cat.
I love this calico cat, but she already has a home. I guess I'll have to pull out my catnapping kit to win her over.