The word originated from the word Fo' Realious (Foe-Real-ee-us). But when one 12 year old on a halo 2 clan forum misspelled it, the word became Forsarelleus (Foe-sa-rel-ee-us)
It is used to verify something that someone says. Its very similar to saying "seriously"
A girl that is short, really pretty, and usually has lighter hair that is extra long. She gets in a lot of trouble but most peoplelove her personality, sometimes. But- this girl has NO common sense what so ever. She loves to party, all the time.
If somebody says something really stupid some peoplemay say you just pulled a tori fanelli; If your turned on by a girl thats pretty you call her a tori fanelli.