Inertia: The inherent property of a body by virtue of which it cannot change its state of rest or of uniform motion until unless a force acts on it.
Different types of inertia:
Inertia of rest: The tendency of a body to remain in its position of rest is called inertia of rest.
Example: While standing in a bus, we fall backward if the bus starts suddenly.
Inertia of motion: The tendency of a body to remain in its state of uniform motion in a straight line is called inertia of motion.
Example: When a running horse stops suddenly, the person sitting in it falls forward.
Inertia of direction: The inability of a body to change its direction of motion by itself is called inertia of direction.
Example: When car takes a sharp turn, a person sitting in the car experience force, acting away from the centre of the curved path. This happens, due to the tendency of a body to hold its original direction.