-) Humiliation of the sub. (submissive, slave)
-) Penetration of the sub. (incl. strap-ons, toys, etc).
-) Bondage / restraint of the sub.
-) "Water Sports"
The dominate one (Madame, Mistress, Domina, Dominatrix, Goddess) have complete control over the slave, such as:
-Riding the slave like a pony
-Put leash and collar on the slave
-Penetrate with strap-on
-Make slaves lick boots
-Dress up slave like a maid,animal, etc.
-Use slave for sexual favors
Some (BAD) dominatrices use slaves as "money slaves", and make them pay for everything. Usually scammers.
Mostly used in sexual games, but some people also have a 24/7 relationship, where the Dominatrix is in charge of her slave/s all the time.
In other words; femdom is most of the time amazing. Check out OWK.cz (Other World Kingdom) for one of the better websites. Other examples are "Whipped Ass" and "Men In Pain".