Adepts, Adepta or Adeptus is the formal title given to the individual Imperial servants of the various departments of the Adeptus Terra that serve the will of the beneficent Emperor. These titles are used by everyone in the service of the Emperor as part of the Imperial service, from high ranking officials to lowly scribes.
It is a great honour to serve the God-Emperor in any capacity and these titles are much respected. Space Marines and Imperial Commanders are entitled to use the honorific "Adeptus" (Adeptus Astartes, Adeptus Administratum, Adeptus Ministorum etc.), as are highborn senior Astra Militarum officers. On Terra and those worlds controlled by the Imperium of Man, the title "Adept" is used for those officials of the Adeptus Terra, primarily the members of the Administratum, who oversee the day-to-day operations of the Imperial bureaucracy.
Those non-specialised workers and labourers, who may be shifted from job-to-job as required, are known instead as "Menials." These often destitute men and women serve as transport drivers, labourers, sanitisers and in other non-skilled but labour-intensive occupations. Menials are recruited from the population of non-Adepts, but take the title Adept themselves. They are very proud of this honour, and will bear almost any indignity to make sure they keep it.
"Adepta" is the feminised version of the title Adept in High Gothic form. This formal title is exclusively used by the all-female monastic orders of the Adepta Sororitas, which includes both the Sororitas' Orders Majoris and Orders Minoris.
- Codex Imperialis (1st Edition), pp. 48-49