A ballistic insert is any bulletproof plate or pad that is not an integral part of the vest. These inserts can be placed inside jackets or carriers or removed if damaged.
Depending on their protection rating, they can be made from a variety of materials. A ballistic insert can be anything from soft fiber armor pads to the toughest Level IV hard plates.
Depending on the size, material, and level of protection, ballistic plates can range from just tens of dollars to multiple hundreds. Hard ballistic plates are the most expensive ones.