In BDSM, TPE refers to a type of relationship: total power exchange. The implication is that the dominant partner has complete control and authority over the submissive in all areas and at all times, even when they're not actively engaged in a scene. Most couples will, however, agree to a set of terms and limits beforehand, which can be renegotiated if it becomes necessary.
It takes a lot of trust to go TPE. I wouldn't give someone that level of control until we'd been together for quite some time!