Service kink a type of role in the BDSM community in which a dominant partner, or top, takes on the role of fulfilling the submissive, or bottom, partner's desires. In essence, the top is servicing the bottom.
More About Service Kink
The role of the service top is controversial in BDSM. Some practitioners will say that service topping is not "real" topping. Those who like service topping say they enjoy the activity. In the typical service topping situation, a bottom asks a top what they want, and the top performs these acts. Bottoms may simply want to receive sensations they like while service tops enjoy providing needed relief to bottoms in those situations.
While some people might interpret this as "topping from the bottom," and not "real" submission, scenes with a service top are generally negotiated and agreed to ahead of time while "topping from the bottom" usually comes as a surprise to the top mid-scene.
While in a scene, it's always the responsibility of the top to monitor the bottom's condition, whether or not there is an established power exchange relationship or not. The same safety rules apply to any scene, whether it's a typical Dom/sub relation or in a servicing situation.
Professional doms are the perfect example of service tops. They are paid to provide a topping service to clients.