A protostar is a young star that is still in the process of formation. There are several synonyms that can be used to describe a protostar, depending on the context. For instance, a protostar could be referred to as a pre-main-sequence star, a stellar embryo, or a star-forming region. Other possible synonyms include proto-sun, protoplanet, and young stellar object. These terms all describe different stages in the formation of a star, and may be used interchangeably depending on the specific details of the stellar system in question. Regardless of which synonym is used, all of these terms refer to a celestial object that is still in the earliest stages of its life.