Noun
flak jacket (plural flak jackets)
A special piece of clothing worn by soldiers to protect them from shrapnel and grenade fragments, other non-direct fire and battlefield debris. Sometimes used informally to connote any of the various forms of a bullet-proof vest.
George Thomas was hit in the chest by an AK-57 round but survived because the shots hit his flak jacket. Source: Internet
When I opened the door I noticed a combat Border Policewoman, 23, wearing a vest and flak jacket. Source: Internet