Subspace is a state of mind associated with BDSM activity. It is a pleasant state of mind that submissives love to experience. It is described as floating or feeling detached. A submissive can enter into subspace as a result of the sensations they get from their Dominant. It is a sense of intense focus, and a submissive can lose awareness of everything going on around them.
The difference between the two ideals.
Different levels of pain
What makes a good Dominance
Machoism and the varying stages of it.
This is a good beginning point.