A submissive is a
person who feels the need to
give up their
rights and
free will to be
controlled by another, ie to submit.
This is most commonly used in a sexual context, but is not necessarily sexual. There are many instances of people who are either very timid or have an extreme fear of rejection or castigation who then choose to let another control their lives, therefore absolving them of any responsibility or ability to make the wrong decision.
Sexually speaking, submissives range anywhere from those who are aroused by the idea that they are under another's control and consider it a bedroom game through the spectrum to the die-hard lifestylists who practice full-out slavery, albeit at the slaves request and consent. Some of these live what is referred to as a Gorean lifestyle after the Gor novels by John Norman.
Unless one is in a Gorean situation, it is the submissive, or bottom, who is actually in control of the action. If things go too far or the submissive becomes too uncomfortable, the action can be stopped at once with the utterance of a safeword or with a signal which has been chosen before the games began. Once it is stopped, it is common for the sub and his or her Dominate to talk things over and find out what was right and what was wrong so that the next time, they can avoid having to stop.
In a Gorean situation, things are rather different, following the ideas expressed in the novels. Yet again, the submissive, or slave, willingly gives themselves to their Master, but in this case it is usually for life and the Master is in complete control, without such things as safewords.
Most submissives consider the act of submitting to be an enriching experience. When one is forced to go beyond the bounds of personal comfort and dignity to satisfy and earn the praise of one that you willingly call Master is said to be an uplifting experience which actually increases self-esteem and reduces personal negativity.