Rubellite is the mineral name for all tourmalines with a reddish tint. As a result, the majority of gem labs certify Red Tourmalines, Pink Tourmalines, and other hues that are similar to "Rubellite Tourmaline." Rubellite, however, is more frequently used in the trade to describe a rare and expensive kind of deep purplish-pink to purplish-red tourmaline.
In other words, the red tourmaline represents what all rubellites are. However, not all red tourmalines are rubellites; only the highest-grade red tourmalines are sold as rubellites.