Bondage is a category of activities that may or may not involve sexual components but always include some form of restraint.
Anyone can engage in the kink, and it is one of the most popular kinks within the BDSM community and most recognizable by those less familiar with BDSM.
Some common types of bondage are:
Rope - There are many styles of rope bondage, most commonly shibari and kinbaku Japanese forms, suspension, and Western bondage. The Japanese styles are focused primarily on artistry and aesthetics, while westernized bondage practices aim for restriction as the main goal. There are a variety of types of rope that one can use, such as hemp, linen, jute, cotton, silk, bamboo, sisal, nylon, and different synthetics. Rope type can effect the comfort and ease of the experience for the bound individual due to the diameter, texture, stretch, braiding, friction, strength, and durability of each type.
Straps and Ties - There are under-the-bed restraint systems that allow a partner to be tied spread eagle on the bed with velcro cuffs. There are sex slings that hang over the door that allow for bondage. These systems are generally more affordable, have a lower learning curve, and are middle-of-the-line in terms of durability.
Devices and Furniture - Spreader bars. Collars and leashes. St. Andrews crosses. Bondage tables and chairs. Bits and gags. Handcuffs. Thigh cuffs. The list continues. All the countless toys, accessories, and larger furniture items are all useful bondage gear.
Mental Bondage - It is always fun to mess with the mind. Playing with the idea of the positions one is allowed to be in can always be fun. You can use simple power exchange and instruction-giving to exercise that control, or you can use the power of suggestion and erotic hypnosis.
Mummification - This is one of the less common, more intense forms of bondage. This is exactly what it sounds like. It involves wrapping a subject from head to toe, much as you would see a mummy, making movement entirely impossible. It causes sensory deprivation and arousing feelings of helplessness for those who enjoy it. Some use ace bandages, while others use vacuum bondage and others go as far as using saran wrap, which can be more risky.
There are special considerations to keep in mind before you get too involved with bondage.
Know your craft. Before restraining anyone or allowing anyone to restrain you, be sure that the rigger is well-versed in any ties and releases they will be using. Many knots are designed to be secure, but also easily removed in case you need to release the bound person.
Learn the risks and precautions. Learn the places on the body that should not be tied or constricted. Learn how to recognize the signs of nerve damage and restricted circulation. Learn your rope bunny's special sensitivities and any issues that may make certain riggings or suspensions unsafe. If you are being bound, communicate anything your rigger should know about orthopedic, circulatory, nervous, and other bodily issues.
Have safety and first aid gear on hand. Always, always, always have safety shears nearby to cut a subject free in case of an emergency! A first aid kit should be on hand at all times as well.
If you are interested in learning more about bondage, here are some good resources to start with:
The Twisted Monk - a nationally-respected Seattle-based rope shop with lots of how-tos and resources for riggers and rope enthusiasts of all kinds
Mummified Techniques - Links to some techniques for more immersive bondage such as sacks, hoods, mummification, cocoons, etc.
Remedial Ropes is devoted to bondage safety and risk awareness-based education for new, experienced and aspiring rope tops and bottoms. These safety basics apply to everything from bedroom bondage to suspension, shibari and inbaku to Western-style. Articles range from very beginner (perfect if your bondage skills begin and end with tying your shoes) to advanced (including busting some extremely common myths about bondage safety).