the female version of "pyro", short for pyromaniac. It means someone who is crazy around fire and likes to light things on fire randomly without any prior consideration or forethought. In other words, ME!!! Which is why my friend Jonathan calls me this all the time.
The girl (ok, me) poured lighter fluid on the picture of her ex-boyfriend, then lit it on fire, which also caused some other things to catch flame. Such as the lawn. When her mother came home and saw what she'd done, she just smiled, gave the girl her medicine, and patted her on the head. "My silly little pyroess," she said.