Super-Size Big Beautiful Woman.

A BBW who is particularly large, more so than a regular BBW. Depending on who you ask, a SSBBW is one who weighs 250 pounds plus, or is more than an XXL.

Super Sized Big Beautiful Woman

Acronym for "Super-Sized Big, Beautiful Woman". A sub-genre of BBW (Big Beautiful Women/Woman) that includes attractive women who typically weigh 400 lbs. or more.

"Super Size Big Beautiful Woman"

A woman who usually weighs over 350lb, found particularly attractive by FAs. Most SSBBW are very hot.

An acronym for Super Smash Brothers Brawl Woman.

SSBBW – Term coined by the fat acceptance movement to denote a women with an amazingly attractive face but possessing a body of astonishing girth and weight (400lbs plus). These women are generally found living lonely and solitary lives gorging them selves while remaining in denial of detrimental effects their extreme size has on their health and personal lives. Those that are lucky enough to attain some form of personal relationships are usually found in the company of small to average sized men with low self esteem and an unhealthy fat or feederism fetish.

It means "Super Size Big Beautiful Woman".

In other words, it is a type of person that is comparative to Big Foot. To better understand:

People say they've seen Big Foot. People say they've seen SSBBWs.

People give vague pictures of Big Foot. People give vague descriptions of SSBBWs.

In both case, neither have been spotted.