A sexuality in which one's sexual attraction changes over time, sometimes on a day to day basis, sometimes over the course of a month, depends on the person for the exact time. In labeling, one might just say they are flexisexual, or put another label for their main or most common attraction, or even put a label for the range their attraction goes through
"I thought she was hetero" "she was yesterday, now she is a lesbian, bet you anything she'll be all over guys again tomorrow, she is flexisexual, her attraction changes over time"
A person of flexible sexual orientation. Whereas they flirt with and try to attract both sexes, yet refuses to identify as bisexual. This person will constantly alter which gender they are more attracted to. Often they will appear to be very androgynous, and hang out with the scene crowd.