A submissive, otherwise known as a sub, is a person who willingly hands over control to a Dominant partner in a play session. Subs can identify as any gender or sexuality. Submission can mean different things to many individuals as every person is different and unique and it can involve many various BDSM activities. Submissives can serve or play with a Mistress or a Master.
Most subs will refer to their Mistress or Master as Ma'am. Mistress, Madam, Sir, or Master. Physical acts can include various types of bondage such as rope, cuffs, caging, or impact play such as spanking, caning, and paddling, as well as different types of torture.
A submissive and a 24/7 slave are different in that a submissive retains their right of choice whilst a slave has consensually agreed to give that right over to their Owner. Slaves become property, whilst submissives do not.