Part- is the smallest portion of an assembly
Assembly-An assembly is collection or grouping of parts designed for a specific function
System-a group of related parts and assemblies that performs a specific job.


Major Systems of a Vehicle
Body and Frame
Engine
Computer Systems
Fuel System
Electrical System
Cooling and Lubrication System
Exhaust and Emission System
Drive Train System
Suspension, Steering and Brake Systems
​Accessory and Safety Systems