Fireplug = fire hydrant

Basically, it's someone who's not fat, but they're a bit shorter than average, their shoulders are a little wider, their waist is a little thicker, their legs are short in proportion to their body and they tend to have muscular thighs.

Oh, and big asses. That's important.

The sweetie in my avatar looks like she's descended from the sort of Teutonic farmwife who could throw a cow over her shoulders and carry it from the field to the barn.

Brooke Haven is another fireplug.