Multigender refers to a person who identifies with more than one gender identity. It can be used as an identity by itself. It can refer to a rainbow of identities, which includes bigender, trigender, quadgender, and pangender. Multigender individuals can identify with two or more genders at the same time, or identity changes can happen over time.
More About Multigender
Being a multigender person does not necessarily reflect in a person's gender expression, sexual identity, or assigned sex. It is something they need to identify as. Gender identity is not always obvious so it's a good idea to ask. Otherwise, it is always safer to just address a person using their name.