Sexual slavery refers to a dominant person owning a submissive person as their property. It is a consensual exchange of power between individuals.
For John and I, sexual slavery works great for me.  As John's Goddess it is his place to make me feel like the Queen that I am.  I consider John more than just my sex slave.  While he does go out of his way to meet my needs sexually, he goes out of his way to meet all my needs.  As my sex slave John has learn to worship my entire body.  

Over the phone, I make men acknowledge my superiority.  I do allow tributes. I allow my callers to serve me in many ways.   A sex slave is often expected to perform many of the same functions that are expected of a slave/submissive, including wearing very revealing clothes, being shared, collar and/or leash, and a variety of other S & M activities.

The duration of this ownership may vary anywhere from a few minutes, as in a scene, to a lifetime commitment.

I do have slave contracts.  They are good for spelling out what is expected of  the slave.  But each contract is individualized, customized to meet my needs.