Is a term used by (usually) pot smokers though it can be used when a group of people are smoking (sharing) anything. The person who "calls" "backs" gets to take second hit. Kind of like calling "shotgun" for passenger seat of a car...
Synonyms for backs
On this page, you will find 30 slang terms related to backs. Some of the top words include: hut, Fire In the Hole, Blaze'n, petro, kill, and 25 more.