Some people use the term "bondage" synonymously with BDSM. It evokes that air of slightly naughty, slightly kinky English eccentricity that is also evoked by talk of spanking or the cane.
Bondage can indeed represent these things and is none the worse for that. However, at its deepest, bondage has the capacity to evoke a profound, sensuous experience like nothing else BDSM can offer. Being constricted to the point at which you cannot move a single part of your body has different effects on different people. Initially most will feel quite anxious at the helplessness, but after time this anxiety gives way to a much more relaxed and serene feeling. Once you learn to give up the struggle and accept that you belong to me, you will start to feel the benefits.
Whether bondage is an end in itself or one of the elements of a more complex session, when you enter my realm of bondage you will only ever be free when you are imprisoned.