1. A sac (bag) of any kind. Could be a backpack, a purse, a plastic bag, a bag for testicles, or any kind of bag/device that holds stuff. See example #1.
2. Loosely used to describe anything. Also used as a suffix for one's name by a small, cultish group of linguists residing in the nation's capital. See example #2.
3. Inserted innocuously into sentences as a substitute for words rhyming with it. See example #3.
SAC means suck.adams.choad... it is a commonly used abrivation. Its somewhat like saying SMD. Or.. in matts word... suck african cock... or suck alotta cream.. but it is again most commonly used as 'Suck Adams Choad'