A submissive renews the choice to submit every time a demand is levied upon her. A slave makes a one-time choice to submit, up front, and thereafter it is incumbent upon her to obey. 

I am fond of this definition because it describes not only my personal experience of submission and slavery, but with some minimal qualification also applies to every submissive or slave relationship. No I am not the person that came up with that bold statement. Back in 1995 well I was still learning the concepts and practices of BDSM I am not the person that came up with that bold statement, The person that came up with that bold statement wasn’t a person by the name of Stephen Davis. Highly respected among the BDSM leather community. I honestly believe when credit is due, I will apply it.
A key elements and being submissive, is the ability to say no. She also has the ability to figure out just how much control she is willing to give up to her partner, the dominant. Now this is also much more of a part time thing this is not a full-time interaction. She does not submit 24/7. Submissive power exchange is about choice: about the option to decide how one feels about a demand and what one is going to do about it. At any point that the sub is not comfortable with this arrangement, it is within hir rights to say "No, I'm not going to do that". If anybody else tells you differently than they have a perverted twist of what BDSM is about.   As to the profiles I’ve been reading lately, people have Mark themselves as a submissive but in their wording in their profiles they clearly are defining themselves as a slave.   I think in short what makes a submissive is: a submissive chooses to submit and has the option in some area or another to say "no" to a dominant command. 
 Now what makes a slave? First and foremost, slavery hinges upon a commitment to obedience. It also comes from internal pleasure, the need and want to pleasing others.The slave does not revisit issues such as "should I submit?" or "How do I feel about that?“ When a Master order is issued, whether or not the slave agrees with it, she is obedient. She is a Obedient because when she committed  to serve she gave her rights to her master to look after, to guide her to protect her. So his word is almost like the law.  A real life style master will never ask or put his sleeve in harms way. He would never dismember her he would never murder her, he would never ask her to do these crazy bizarre things like involve children or animals. Same people don’t do these things. 
 People that call themselves a master that read these perverted stories over and over again and watch these super intense videos are the ones that you need to be wary about.  It doesn’t mean that something that you have watched in a video cannot be truly performed within the BDSM lifestyle. But it doesn’t mean because someone weird perverse guy spent 190 hours watching porn movies about BDSM that makes him a master. You earn generally the title of a master among your peers. Because when you do that you have mastered certain skills that the community recognizes. 
 While both slaves and submissives are often fondly referred to as "property", in the sense of consensual slavery the slave becomes literally (by mutual agreement) the property of the Owner.  A brief summary of what people don’t understand, is as a slave cannot say "No" without completely abrogating the very basis of the Master/slave agreement. A "No" from a slave is a terminal deal-breaker in a way that it is not for a submissive.  There are many ways to try to put this in easy perspective. One would be is any job out there whether it’s an office setting whether your waitressing, anything and you have a boss. Your boss gives you a task to do. And you can sit and weigh the options of doing the task basically if you don’t do it that is like saying no. You decided that you did not want to do the task. So you didn’t do it. You can protest directives, you can discuss the matter more. But that basically does not happen when you are a slave. A slave, on the other hand, Is much more as in a controlled environment say like the military, when your commander gives you an order, it gets done. So if she disobeys orders, has put herself in a position of mutiny with much more dire consequences to her relationship. Slavery is not about submission or submissive behaviors. It is about obedience and it is about the ultimate commitment of service to your Master. 
A slave is a separate dynamic then a submissive.  A slave holds no limits other than what their Masters give them. They can not refuse service to their Master. Some consider themselves property of their Masters. Every aspect of the slave’s life may be controlled by the Master. The Master works with-in the preset limits established at the start of the relationship. The slave does not get to take advantage of things like sitting in a chair instead of on the floor, choosing your own clothes each day or listening to their favorite music. These things serve as a reward to a slave, only given when the Master feels that the slave deserving of it. You have no rights as a slave. Every part of your day is controlled by your Master. 
I hope that the information I am providing here for you gives you a little bit more in depth that when you write your profile and you want to become property. And you want to enjoy slavery that you understand  just what you were asking for. Because those of us that are looking for a slave or looking for those key qualities. And when you list yourself as a submissive but have sleeve qualities 9 times out of 10 we are going to pursue you because we know not necessarily what’s going to be better for you but based upon your wording you’ve already told us what you were truly looking for.