In the context of Containment Fiction, Group(s) or Person(s) of Interest is an in-universe actor which exists to serve either as a protagonist or antagonist of the fiction depending on the perspective from which it is being written. They do not necessarily have to be actual groups, as some (Such as the SCP Wiki’s “Nobody”) are single individuals or decentralized groups (Are We Cool Yet?, Gamers Against Weed).
The original conceit of “groups of interest” within the confic space were created by Dr. Gears, Kain Pathos Crow, and Bijhan on the WikiDot-based SCP Wiki in 2008. They were a mix of groups which actually existed in the real world being fictionalized, such as the Iranian Revolutionary Guard, and entirely fictional concepts such as the Church of the Broken God.
While the concept was originally developed in a formal way on the SCP Wiki, it has spread to be used across all major containment fiction spaces, even if it is only done nominally. Groups of Interest as a formal concept are not considered to be an integral part of containment fiction but they are a common phenomenon whether through independent innovation or through copying what SCP did.
SCP Foundation Groups of Interest
SCP Foundation Groups of Interest Formatted Confic
RPC Authority Alternate Realities
Chaos Insurgency Wiki GoI Page
Backrooms/Tech Support Persons of Interest