Abbreviation for "pyromaniacs". People who are fascinated and intrigued by fire and burning. A pyro may spend a great deal of time experimenting with and playing with fire.
Don't give her your lighter, man, she's a pyro.
Young, anti-social individuals who like to play with no one and nothing but fire and firearms.
Oklahoma Bombmer Timothy McVeigh.
All lead characters in cult classic Romper Stomper (staring Russell Crowe).