What condition distinguishes a Protostar from a true star?

Answer

Its core temperature has not reached the threshold for sustained nuclear fusion.

A Protostar is a hot, dense, collapsing core that glows due to gravitational contraction, but it is not yet a true star because its core temperature is insufficient to ignite sustained nuclear fusion.

What condition distinguishes a Protostar from a true star?
astronomylife cyclestarstellar evolutionmassive stars