The act of performing services for the Dominant, in a power exchange relationship.
This is where the submissive performs service related tasks, outside of just sexual servicing for the dominant of the relationship.
Pleasure is derived more from the act of pleasing their dominant, rather than the task itself.
This can include playing the role of Butler, Maid, or other roles, within a relationship.
Noteworthy:There are some instances, in which the submissive will hide their servitude, or pleasure gained from such 'service' or do so to heighten a particular fetish.
Many in the BDSM community frown on this hiding of pleasure, from service, as it can conflict with the concept of 'consent'.
Some use their servitude to further their own fetish tastes, such as those who will rub a dominants foot, as a service, but secretly enjoy the touch of feet, due to having a foot fetish.