What does AJ stand for?

Anal Job

"Anal Job" is a colloquial and often crude term that refers to anal sex. It is a direct and explicit descriptor of sexual penetration of the anus. This abbreviation is frequently used to categorize or search for specific types of adult content, or to describe sexual preferences and activities in a concise manner within adult-oriented discussions. Like many such terms, it is used for brevity in contexts where explicit language is common.