A radio star (stellar radio source or radio source star) is a star that emits a lot of radio, either constant or pulsed. Different kinds of stars fit this criteria, including pulsars, and rotating radio transients, which are also a type of neutron star.
Late-type stars may also produce masers. The Sun produces some radio waves but not enough to be considered a radio star.
Quasars are not stars, thus a quasar radio source is not a radio star.