A bangle is a type of bracelet that is formed as a single ring. It typically has no opening and is put on by compressing the hand, thumb to little finger, and slipping the bracelet over the wrist. The width of the hand keeps the bangle from falling off.
Bangles are probably the oldest form of jewelry, and can be made out of any material that can hold a stiff form: wood, plastic, paper mache and of course, precious metals such as gold. In some primitive societies, the family's wealth was stored and transported as bangles and necklaces worn by the women. The more gold bangles you could stack up your arm, the higher status you could be presumed to hold.
A bangle can be worn alone or in large clattering groups. The word bangle itself can mean 'simple adornment' or 'cheap trinket' depending upon the context; for instance, "Her simple twin set and single gold bangle completed the ivy-league look" versus "Plastic dimestore bangles adorned her sunburned wrists, clattering as she played inexpertly with her cigarette holder."
If wearing several bangles, combine styles with care. A gold bangle among wooden ones can look startling, or simply confused. A wooden bangle, perhaps stained with leopard spots, can go with a funky or ethnic look, but might jar if worn with Harris tweed.
A glass bangle might be beautiful, particularly one made of strands of colored glass fused together, but be wary. A door closing too soon or a sudden jar from a car door and you might be looking at shards embedded in your wrist. Stick with Lucite or acrylic if you like the clear bangle concept.
A bangle can be plain, just a ring of plastic, gold or other material, or carved into interesting shapes, or bejeweled and faceted. Bangles are never out of fashion, so a large collection of bangles in different materials, colors and styles can serve you well for many years.