If your cat's abscess bursts, that yellow goo you see oozing out of it is pus. Take Fluffy to the vet to treat the infection.
Feline mouths are chock full of nasty bacteria. That's why a cat-bite wound so often results in an abscess. The abscess forms from the infection, creating a cavity full of pus. The majority of cat bites occur on the face, tail and shoulders. While most abscesses heal up well, your cat could have been exposed to the feline leukemia or feline immunodeficiency virus through the bite. These diseases are usually fatal.
Before your cat's abscess bursts, that infection was brewing in his body. Abscesses are painful, so Fluffy might have lost his appetite or run a fever. Within two days to a week after his bite injury, the site begins to swell. It can become quite large. It's sensitive, so be careful touching it and wear rubber gloves. The lump usually feels soft and warm. If you don't take him to the vet to have it lanced, it can burst from the pressure. An incredible amount of stinky yellow pus and blood can ooze out of the abscess. Once it bursts, you'll see a hole where the abscess used to be.
If the abscess hasn't burst, your vet will likely shave the area and lance it to get rid of the pus. If it has burst, she'll flush it out. She might sedate your cat to make it easier on him and her, especially if the abscess is exceptionally big or painful. Those might also require the vet to insert a drain for a few days to make sure all the pus comes out. Your vet will show you how flush and disinfect it and prescribe antibiotics for the infection. You must make sure the wound stays open so it can drain. It could take your kitty a week or more to heal. If he's not better in a week, or if the infection recurs, take him back to the vet.
The best way to prevent future abscesses is by having your fighting feline friend neutered and keeping him indoors. Tomcats are the most frequent victims of abscesses because they fight other cats over territory. That doesn't mean your neutered, indoor cat won't get into a fight with one of his kitty housemates, but it's less likely. If you witness your cat getting into a fight and being bitten, take him to the vet immediately for an examination. She might prescribe antibiotics that can stop the infection from starting.