"Kinning for Fun"

The accepted definition of otherkin is "a person that identifies wholly or partially as nonhuman or as a fictional entity, on a nonphysical, involuntary, and profound level".

The common misconception among younger people, primarily on twitter, instagram, and tiktok, is that it's just a character that you like a lot or relate to, which are a different set of terms entirely.
Some of them come under the wider Alterhuman label (but sometimes it's just bad phrasing of saying that they like a character), but they're not the same thing as being otherkin. The 'Kin Definitions and the Alterhuman Definitions links on the last page are comprehensive lists of various terms, but the four most common terms for a voluntary and/or an "identify with" identity are otherhearted, otherlink, synpath, and kith. These all have slightly different definitions and connotations.

This is a very brief description of these terms, and some context and the sources for who coined these terms (where applicable) are in the links at the side. Most of the descriptions here are just the commonly accepted definitions or from the Alterhuman Definitions directly, just so they're easier to find right here on the page rather than scrolling through the entire wiki to find these four terms.

Otherlink: Otherlink is the term for voluntarily choosing a nonhuman or fictional identity. As they're voluntary (unlike being otherkin), links can be dropped voluntarily.
Kith: A strong identification with or a connection to a nonhuman creature or fictional character. (As opposed to Otherkin, which is identifying as.)
Otherhearted: Identifying with a non human or fictional being, but still on a profound and integral level. Although hearttypes differ from kintypes in that being otherhearted is identifying with a being, as opposed to otherkin identifying as a being, being otherhearted is still profound, and generally considered to be involuntary.
Synpath: Having a strong connection to an entity, but not identifying as them. Very similar to otherhearted, but they're phrased differently, eg. [Entity]hearted vs [Entity] is my synpath.

Copinglink: There's another term, copinglink, which is a term for voluntarily choosing a nonhuman or fictional identity as a coping method.

Also, just because most "kin for fun" people are often likened to otherlink if they even are alterhuman, that absolutely does not mean that otherlinkers are the same as the poeple who "kin for fun". Otherlinkers are just as alterhuman as otherkin are. The issue is people using otherkin terms to describe a voluntary experience, or sometimes even just liking a character. Many people who "kin for fun" are just fans of the character, or just roleplay them often, which wouldn't fit under any of the alterhuman terms. Especially so when they know about terms like otherlinking and still choose to use otherkin terminology.