Love Robin MIGHT ALLOW use of select fanon concepts on this page; CONTACT them to discuss requirements and details
Idem is Latin, meaning "the same". It and its shortened "Id" are literary terms used to denote "same as the previously cited source". Normally it is particularly used in legal citations.
As used in Love Robin's Every Kim Possible series of continuities, when multiverse travel first started in what is now the multi-dimensional super-civilization known as the Combined Crosstime Continuums, and the discovery of alternate universes, each inhabited with nearly identical people, the term "Idem" was co-opted to mean "a person's dimensional alternate".