Sith Acolyte was a rank within the Sith Order prior to Darth Bane’s reformation. The term was used to refer to Force-sensitive apprentices who had only just started on the dark path under the tutelage of a more experienced Sith Lord to rightfully bear the mantle of Sith.
The redeemed Revan encountered several Sith Acolytes in the Temple of the Ancients on Lehon. These acolytes were trained under Darth Malak and studied the dark side of the Force in secret, guarded by a force field outside the temple.
During the time of the Reconstituted Sith Empire, acolytes were tested by Sith Overseers before earning their place as proper apprentices under a superior Sith Lord.
Acolytes were trained by the Brotherhood of Darkness at the Dathomir Academy and the Iridonia Academy.
The character Gamblor, a Hutt Sith Acolyte, featured in Juo Deltar Faces Gamblor the Terrible, a holovid that was produced during the waning years of the Galactic Republic.
Galen Marek was also loosely referred to as a Sith Acolyte due to his apprenticeship under Darth Vader, who already had a master. Marek’s clone encountered Imperial Sith Acolytes during his quest to find Juno Eclipse. These Sith Acolytes were trained on Kamino.
The rank was also used by Darth Krayt‘s reformed Order. Its use may have been similar to that of the earlier Sith. Krayt referred to himself as a Sith Acolyte in his apprenticeship under XoXaan on Korriban.