Definition of: inertia

(in·ûr′shə) noun
1. The state of being inert; sluggishness.
2. Physics a That property of matter by virtue of which any physical body persists in its state of rest or of uniform motion until acted upon by some external force; its quantitative expression is mass. b A similar property noted in certain forms of energy, as electricity and quanta. [<L, idleness]
—in·er′tial adjective