Sith acolyte was a designation given to Force-sensitives who existed outside the established Sith Master and Sith apprentice dynamic dictated by the Rule of Two. They were intended to be trained as a subordinate agent, not considered a true Sith, but still expected to adhere to their tradition.
Revan, after his redemption, came across several Sith acolytes within the Temple of the Ancients situated on Lehon. These acolytes received instruction from Darth Malak and secretly delved into the dark side of the Force, their activities shielded by a force field surrounding the temple.
During the era of the Reconstituted Sith Empire, aspiring acolytes faced trials administered by Sith Overseers as a prerequisite to earning a place as a proper apprentices under a superior Sith Lord.
The Brotherhood of Darkness provided training to acolytes at both the Dathomir Academy and the Iridonia Academy.
The character known as Gamblor, a Hutt Sith Acolyte, was a key figure in Juo Deltar Faces Gamblor the Terrible, a holovid produced towards the end of the Galactic Republic period.
Asajj Ventress held the title of Sith acolyte. Galen Marek was also informally called a Sith acolyte due to his apprenticeship with Darth Vader, who already had an established master. Marek's clone encountered Imperial Sith Acolytes while searching for Juno Eclipse. These Sith Acolytes received their training on Kamino.
Darth Krayt's reorganized Order also utilized this rank. Their usage of it might have mirrored that of earlier Sith traditions. Krayt himself was referred to as a Sith Acolyte during his apprenticeship under XoXaan on Korriban.