A
Pegasus is a male unicorn. Colloquial; Synonym for hot bi guy or
HBG, often derogatory, condescending, or ironic. A bisexual person, who is willing to join an existing couple, often with the presumption that this person will date and become sexually involved with both members of that couple, and not demand anything or do anything which might cause problems or inconvenience to that couple.
The term is often used to be dismissive of a couple seen to be only superficially
polyamorous. Because of the demands that this type of couple places on the woman (that he be single and not take on any additional partners, and become involved with both members of the couple equally, and often "complete" their family as a
sperm donor and not do anything that may threaten or disrupt the existing couple), many in
the poly community call this type of man a "Pegasus", as in mythical and not likely to be found.
Jim wife wants a single, attractive man who will love and have sex equally with both and her husband, but not interfere with their marriage,
move in together, help raise their kids; and not have any other partners. she's looking for something that doesn't exist.
Jims wife wants a pegasus. A male unicorn to for fill both of their sexual desires and possibly even
impregnate her due to their long standing
fertility issues.