Phys.org
Protostar
A star that is still assembling itself and has not yet started fusion.
A collapsing core of a molecular cloud heats as it contracts, glowing in the infrared from gravitational energy alone. Material spirals in through a disc and a good deal of it is thrown back out along the poles as jets, which is how these objects are usually spotted — the jets are visible where the protostar is not. The phase lasts a few hundred thousand years, ending when the core reaches about ten million kelvin and hydrogen fusion begins, which halts the collapse.
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Related terms
Magnetar
A neutron star with a magnetic field a thousand trillion times Earth's.
Supernova (Type Ia and Type II)
Two unrelated ways for a star to explode, useful for two entirely different reasons.
The main sequence
The long, stable middle age a star spends fusing hydrogen in its core.
Hertzsprung–Russell diagram
The single plot that organises everything about stars.
Questions
What is Protostar?
A star that is still assembling itself and has not yet started fusion.
Why does it matter?
Material spirals in through a disc and a good deal of it is thrown back out along the poles as jets, which is how these objects are usually spotted — the jets are visible where the protostar is not. The phase lasts a few hundred thousand years, ending when the core reaches about ten million kelvin and hydrogen fusion begins, which halts the collapse.