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.
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.
The it/its lesbian flags were coined by Tumblr user ultbee on February 3rd, 2019. They have no confirmed meaning.