A cat is a domesticated feline.
When Blu and Jewel are running on the street while Nigel, Armando, and Tipa chase them, they spy a cat (referred to as "Clyde" in the model sheets). Blu then makes a dog's barking noise to scare the cat, causing it to jump and attack Armando and Tipa.
The cat was also a deleted character named Cylde, who was owned by Linda's aunt. They were seen at the vet.
In the final draft of the movie, he is a stray.