| Ae and Be stars | Pre–main sequence stars more massive than 3 solarmasses (M_).
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| association | A group of stars whose gravity is insufficient to hold it together but has not yet had time to disperse.
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| bipolar outflow | Relatively narrow beams of matter ejected in opposite directions by a protostar.
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| cloud core | The dense part of a molecular cloud where star formation takes place.
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| giant molecular cloud | An unusually large molecular cloud that may contain as much as 1 million M_.
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| Herbig-Haro object | A clump of gas illuminated by a jet of matter streaming away from a young star.
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| molecular cloud | A relatively dense, cool interstellar cloud in which molecules are common.
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| planetesimal | A primordial solar system body of intermediate size that accreted with other planetesimals to form planets and satellites.
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| protostar | A star in the process of formation.
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| solar nebula | The rotating disk of gas and dust, surrounding the newly formed Sun, from which planets and smaller solar system bodies formed.
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| T Tauri star | A pre–main sequence star, less massive than about three solar masses, showing intense emission lines.
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