Sith Master

The Sith master was a title given to a Sith when he had supreme leadership over the Sith. Before Darth Bane bestowed the Rule of Two, lots of Sith claimed themselves as a Sith master, but when the Rule of Two was bestowed, it meant that there could only be two Sith Masters at a time in the Universe.

Apprentices
A Sith Master's apprentice a Sith following the path of his or her master.