In this form of sexual slavery as it pertains to BDSM, slavery refers to a dominant person owning a submissive person as property. It is a consensual exchange of power between individuals.

In the erotic or lifestyle context of "Dominance and submission" (also known as D&s, Ds or D/s) the types of activities entered into are usually well defined in advance and sometimes spelled out in a so called 'slave contract', a non-legally binding document that outlines the desires, limits, and expectations of all involved.
Typically outlined are clear expectations whether the couple will be monogamous or polyamorous, and if there would be permission/expectations of sexual interaction with other people.
Otherwise, a sex slave is often expected to perform many of the same functions that are expected of a submissive, including wearing very revealing clothes, collar and/or leash, being shared, engaging in S&M or bondage activities.