An inertial frame of reference = constant vel.

non inertial frame of reference = acceleration

Is earth an inertia or non inertial frame of reference? plz do reply as soon as possible

No, an inertial reference frame is not an absolute reference frame. It is a frame of reference in which an object either remains at rest or moves with constant velocity in a straight line, but it is not considered absolute as its motion can be affected by external forces.

An inertial frame of reference (FOR) is a non-accelerating FOR , for example if a person is observing a moving car while at rest or while moving at constant velocity, he is in an inertial FOR. A non-inertial frame of reference is an accelerating FOR for example a rotating FOR. ( Rotation requires centripetal force and centripetal acceleration so any rotating object always requires a centripetal acceleration to rotate.)

It says that the speed of light in a vacuum measured in any inertial frame of reference is equivalent to the speed of light in a vacuum measured in any other inertial frame of reference.