Ballast is a friendly reference to; a mate, sidekick, wife, bitch, girlfriend, boyfriend, trick, pal, etc. but especially the person who rides shotgun with them in their car.
Used by Eddie Haskel to describe Lumpy in an episode of "Leave It To Beaver".
A derogatory name given to a person who is withholding a comment/skill/resource in order to purposefully change the atmosphere in which he is residing by then revealing the sandbagged item.
A person who is a Ballast is one who pretends to have no Snickers when asked, but really does and is just waiting to lower the general mood of his surroundings with the no, then appear bring the mood that much higher when the hidden Snickers have been revealed.
The least attractive female in a group of females. Normally, femalefriends/aquaintances like to attach ballast to their group to make themselves look better.
Tom: Hey Rob check out that group of hotties over there by the bar.
Rob: Yeah but the one with the huge funbags is so ballast.