An it/its lesbian or itsbian refers to a lesbian who uses it/its pronouns. Those pronouns can be exclusive or part of a multipronoun set. It is a more specific form of pronoun non-conformity and crosspronoun usage.
Neopronoun gays, neopronoun lesbians, he/him lesbians, she/her gays, they/them lesbians, it/its gay people and they/them gay identities exist through the same principle.
History
It is unknown when this term was coined, however it has been used amongst the community for many years alongside terms such as he/him lesbian.
Flag
The it/its lesbian flags were coined by Tumblr user ultbee on February 3rd, 2019. They have no confirmed meaning.
Resources
https://pronoun-archive.tumblr.com/post/182527541061/now-presenting-the-itits-lesbian-flags-for-
Third flag.
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Fourth flag.