Formal:
* Ailurophile: This is the most common and accurate term, derived from the Greek words "ailouros" (cat) and "philos" (lover).
* Cat enthusiast: This is a more general and neutral term.
Informal:
* Cat person: This is the most common and informal way to describe someone who loves cats.
* Cat lover: This is another common and informal way to describe someone who loves cats.
* Crazy cat lady/man: This term is often used jokingly, but can be considered offensive or stereotypical.
* Cat fanatic: This term implies a strong passion for cats.
Ultimately, the best way to describe someone who loves cats depends on the context and the tone you want to convey.