Often used pejoratively to refer to a promiscuous woman.
Ayer, conocí a una fulana que me contó historias fascinantes sobre su vida.
Yesterday, I met a so-and-so who told me fascinating stories about her life.
¿Quién es esa fulana que siempre llega tarde a las reuniones?
Who is that so-and-so who always arrives late to the meetings?