A word commonly used to describe a person, mostly women, who have a big butt. This butt has a very big "span" and is usually found on people who are overweight.
LaShonday: "DAAAAMN BONIFA! DID YOU SEE THAT SPANTAAANEOUS BOOTAY?"
Bonifa: "OH MA GAAD! THE GIRL FROM PRECIOUS!!!" *runs up to Spantaneous Bootay*
Bonifa:"OH SHIIIT! DATS A DUUDE!"