A Protostar is an early stage in the development of a star, formed from a contracting giant Molecular Cloud and eventually (on the order of 10 million years) becoming a T-Tauri Star (TTS) or other type of Pre-Main-Sequence Star (PMS). The protostar is heated by the release of gravitational energy as the gas contracts rather than by fusion. It will eventually ignite fusion and become a Main Sequence Star.
Cold Mass Accretion (CMA)
Herschel Orion Protostar Survey (HOPS)
Pre-Main-Sequence Star (PMS)
Star-Forming Region (SFR)
Young Stellar Object (YSO)