Term used to describe a well endowed male or female.
When used to describe a women, it generally refers to a large set of Breasts. It denotes an enormous set, more than normal.
When applied to a Male, it refers to an extra large sized penis, both in length and girth, or either.
Mainly used for those who are above average in length, such as a person with a 7 inch penis could be called 'stacked'.