What is the inertial

relating to or arising from inertia.

"high-speed centrifuges generate large inertial forces"

(of navigation or guidance) depending on internal instruments which measure a craft's acceleration and compare the calculated position with stored data.

(of a frame of reference) in which bodies continue at rest or in uniform straight motion unless acted on by a force.

"the laws of physics take the same form in all inertial frames"