Newton\’s first law of motion is also called as law of inertia.
Inertia means register to change. The inherent property of a material body by virtue of which it cannot change by itself its state of rest or of uniform motion in a straight line

it is the natural tendency of an object ,so that if an object is in rest it tends be in rest or if an object is in motion it tends be in motion
The natural tendency of an object to resist a change in its shape is called inertia .
The tendency of an object to remain in its present state of rest or motion is known as law of inertia.
The inability of an object to change its direction , motoin
The tendency of an object is called inertia

According to this law , any body remains in its state of rest or motion until there is no external applied on body.