Definitions for "Firestop"
cat or other blocking place in walls to prevent a flue effect. Cement or metal firestops are occasionally required by some building code.
Wood blocking, usually 2X4, used to retard the spread of fire, and installed between studding. Required by building codes in some areas, expecially for ballon framing.
Any solid object used to block airways between walls to prevent smoke and fire from spreading.