Anal
penetration that ascends beyond the rectum and into the large intestine.
"endo" is known from
medical terminology for something inside the human body and "a-z" indicates that it goes through the rectum from one end to the other as the letters are the start and end of the alphabet and being pronounced as "ass".
The term originates at the Arizona Endocrinology Center which abbreviates its name to Azendo, an apparent pun on the Arizona state
abbreviation "AZ".