Messenger Bag (n.)
A cloth sack that is strapped around the front of the chest and worn on the back.
Most commonly used for messengers on bicycles. The design allows for quick access to the contents inside the bag by simply rotating the strap bringing the sack to the front.
Messenger bags (also called “courier bags”) are casual such that they should not be worn with any professional clothing (suits, overcoats, etc.) or be used by anyone except messengers.
Example of a messenger bag for men:
