A blunt and/or blunt wrap. A pocket can be a marijuana-filled blunt, or just the wrap (or cigarillo) itself. The name is referenced to the wrap's "pocket-like holding ability". Generally, a common pocket is filled with a gram of delicious dro and smoked amongst a few friends.
The origin of the name pocket refers to the first lines of the song "The Good Times Are Killing Me" by Modest Mouse.
In American football, the pocket refers to the horse-shoe shaped area formed by offensive lineman to protect the quarterback during a passing play. If the lineman do their job, the pocket will protect the QB long enough for him to find an open receiver and throw. If a defensive player penetrates the pocket too quickly, the QB will likely get sacked.