>>4714BBA is old hag; granny. BBA is a shorthand for 婆あ or "babaa"; it's essentially a pejorative of お婆さん or "obaa-san". Obaa-san is polite to use, Babaa will turn a happy old lady into a sad cranky one as illustrated in this image.
>>4716Three letters because 婆 reads as ババ "baba", and あ is just "a". So babaa -> BaBaA -> BBA.