Alpha/Beta/Omega, also known as a/b/o is a kink trope wherein the characters who are mostly human, have defined biological features and roles based on a hierarchical system.
There may be werewolf or knotting (Knotting is a kink based on the bulbus glandis), or it might be that the characters are purely human.
The term “a/b/o” is mainly written with slashes in between the words, otherwise it would overlap with an Australian slur for aboriginal people.
“A / B / O” is often regarded as a fanfiction trope, but fanart is also accessible.
“Alpha / Beta / Omega” originally comes from the American television series, Supernatural fandom, while individual components of the theme existed much earlier.
The very first was made in May 2010 and was also named as the culprit responsible for the success of knotting in “a / b / o” fanfictions.
It also found its way to Japanese fandoms around 2014 through both doujins and fanart featuring the kink trope on Pixiv.
The kink trope spread rapidly beyond the Supernatural fandom, and now it gained itself a global presence.
Also, as of 2019 “a/b/o” content became so popular in Japan, that some stores have started creating displays populated with “a/b/o” works.