Linked from
The 20 pages that link to Protostar, each with the reason it gives.
Stellar evolutionBroader topic: It is an early stage between a collapsing cloud and a stable star.
Molecular cloudBroader topic: Protostars emerge from collapsing cores within molecular clouds.
StarBroader topic: A protostar is the direct precursor to a stable, hydrogen-burning star.
Bok globuleBroader topic: A collapsing globule can produce a protostar at its center.
Prestellar coreBroader topic: A collapsing prestellar core can develop into this next stage.