Scientific meaning: Inertia is described as resistance to alteration of its condition of movement, mobile or inert. Meaning that if an object is moving at 100kmh, it would require a force of greater than that to move it. If the object is immobile, it will require a force sufficient to move its mass.

Common usage, applied to people: Inertia means a state of idleness, or unchanging condition, usually a derogatory expression.