Definition - What does Immobilization mean?
Immobilization refers to any form of bondage that immobilizes the submissive. This can be through the use of ropes, harnesses and chains, as well as dungeon and other BDSM equipment. In the strictest sense, however, immobilization is seen as an extreme form of bondage where any kind of movement is impossible. It is complete submission to a dominant partner.
Kinkly explains Immobilization
Immobilization is perhaps the most extreme position for a submissive to be in. It can be very fulfilling for anyone who longs for “ultimate” submission. Of course, this shouldn't be done with just anyone. It is a dangerous practice. Long periods of immobilization can use nervous and muscular problems, among others. A trustworthy and conscientious partner is necessary.