Final answer:
Crate engines are complete engine assemblies designed for older vehicles or competition vehicles used on tracks or off-road, not subject to current emission regulations.
Step-by-step explanation:
Crate are complete engine assemblies that can be installed in a vehicle.
They are designed for vehicles manufactured before current emission regulations were established, or for competition vehicles that are driven on tracks or off-road.
These engines are commonly used for restoration of classic cars, muscle cars, and hot rods, or for building high-performance competition vehicles that don't need to comply with street legal emission standards.
Crate engines come in various configurations and performance levels to suit different applications.