Wikipedia
Self-bondage refers to the use of restraints on oneself for erotic pleasure. It is a form of erotic bondage which can be practiced alone.
Self-bondage is characterized by experimentation and ingenuity, and can be riskier than conventional bondage. Self-bondage requires use of techniques for self-binding as movement becomes increasingly restricted as more restraints are applied, and also requires a reliable release mechanism. Many types of bondage equipment can be applied before the one that restrains the hands. For example, leg irons can be applied, as well as gags, blindfolds, etc.
For many of its practitioners, the added challenges and dangers are a part of the appeal of self-bondage, who often devise elaborate self-bondage schemes and release mechanisms, both in practice and in erotic fiction.