please note that this is far from an exhaustive glossary of terms; i'm only defining ones that may show up on this site.
alterhuman: a person who identifies outside of the usual, socially-accepted idea of "human."
dysphoria: a state of unease or distress. some alterhumans experience species dysphoria.
fictionkin: a person who identifies with/as something/someone fictional. the identity can be as a specific character or as a member of a fictional race or species.
(other-, fiction-, animal-)hearted: an identity often described as identifying with something, as opposed to otherkin where you identify as it.
nonhuman: used interchangably; refers to both literal nonhuman animals and to nonhuman identity in an "umbrella term" sort of way.
otherkin: a person who identifies as something nonhuman.
shifting: a state in which someone feels that they are more in the mindset of their kintype than usual.
therianthrope: a person who identifies in some way as an earthly animal.
transspecies: a label sometimes adopted by alterhuman folk, especially ones who experience dyspohria.