The practice of covering a person's eyes while engaging in sex or sexual related activity.
Depending on the type of blindfold uses, it is to restrict, if not completely, eliminate a persons ability to see their surroundings.
Some blindfolds are applied while the subject has their eyes shut tight, and these particular implements not only prevent one from seeing, but from also opening their eyes.
Most blindfolds however, simply restrict one's vision, whether the eyes are open or shut.
To inhibit one's vision, so that they are forced to rely on their other senses during sexual acts, foreplay.
Being bound is not a requirement, though often accompanies such role playing, in order to heighten the thrill, or the excitement of sex.
There are various means of blindfolding, using different clothes. Some are more restrictive, while some allow for some light to penetrate. However the goal of any good blindfold is to prevent any vision of what is happening.
Masks, used for sleeping are considered good blindfolds, as they block out all forms of vision.
Other materials that can be used, are a towel, a shirt, anything that can be placed over the eyes, and tied off so as to not fall off during any type of violent head motion.
The goal is to create a situation where the blindfolded person is unaware of what is about to happen, until it does. This increases the sexual pleasures, and the associated feelings.
Simple touching can become far more erotic, more sensual when one party is blindfolded, forced to rely on their other senses.
Used more in BDSM role playing, it is still popular in the more vanilla type of sex.
Practice (Associated Acts): Martial Arts and Weight Lifting use blindfolds, in order to force one to rely on their other senses, such as sound, touch, smell.
Noteworthy: Before the advent of sunglasses, blindfolds were used by Blind People, to show their inability to see. While it is not very common anymore, thanks to sunglasses, it is still practiced by some persons with loss of vision.
Used in children games, parlor games such as mind reading, guessing games, and also in meditation.
Under such use, meditation, the goal is to allow the person to focus on their self, on their own thoughts, which is similar to it's use in sexual situations.
Used to hide the identity of a person, during a hostage or kidnapping situation.