Meaning

verb identify as in botany or biology, for example

verb provide with a key

verb vandalize a car by scratching the sides with a key

origin* (praiseworthy and admirable): Coined by 4chan users upset at the widened usage of based (“praiseworthy and admirable, particularly in a perceived countercultural sense”) outside of their community. Most likely simply from the verb key; in slang perhaps connected to the "securing" action of a lock and key (compare e.g. scored).

Etymology from Wiktionary, CC BY-SA 3.0