Pseudo-incest 

Sex with someone with a familial relationship, but no blood relationship. Sometimes treated as incest in the law, but not as much of a taboo subject in common society.

"Dude, she's not my mom! She just married my father."
"So that's pseudo-incest. Still illegal in this state."

Pseudo-incest by Stevarooni September 11, 2016

Pseudo-Incest 

In literature, any book that contains some form of explicit content (such as romance or sexual activity).

In crime, the act of sexual activity involving non-genetically-related family members (Such as step-family or adoptive-family members).

(Literature) My friend is reading a book which contains pseudo-incest. They said that it's a good book so far!

(Crime) My uncle is going to court for his two acts of pseudo-incest, having sex with his adoptive niece and his stepmother.

Pseudo-Incest by Alan T. Fitch May 3, 2022

psuedo-incest 

Sexual relations with someone you consider as close as a family member, but who is not legally your relative. May feel awkwardly like regular incest, but is generally more socially accepted.

Person 1: So like... me and Mike have known each other for a while... but he's like a brother to me, if I bang him won't that be wrong?

Person 2: Naw, that's only psuedo-incest, go get yourself a piece o' his sausage.

psuedo-incest by Fatality January 10, 2006