Definitions for "Lag Screw"
A screw, usually 1/4 inch in diameter or larger, with a hexagonal head that can be screwed in with an adjustable or socket wrench. Home Improvement Encyclopedia
A screw that produces compression on fixation because of partial threading (at the distal part of the screw)
A large screw, usually 4 inches or longer, with a hex head, turned with a wrench.