People who identify as gender fluid come under the gender queer or non-binary category where in they don't have constant gender.

 

This art installation is a representation of gender fluidity. The white and black bones represent masculinity and femininity respectively. All the bones also represent different aspects of a person such as personality, sexual orientation, etc. 

When all of these mix together, they make a person. The one who is comfortable in what they are irrespective of their gender.