The word "af" appears to be a typo or an incomplete form. It is often used in informal English, particularly in online contexts, as an abbreviation for "as f***," which is a slang expression used to emphasize an extreme degree of something. For example, saying "I'm hungry af" means "I'm very hungry."
The abbreviation "af" is derived from a colloquial phrase that became popular in internet slang and social media as a means of expressing emphasis or intensity. The phrase it abbreviates includes a profanity, which is often used to convey strong feelings.