Polka dots are a series of circles of of different shapes (and often colors) that are spaced out in an even pattern.
Polka dots were originally worn by flamenco dancers and other performers. They briefly came into popularity during the late 19th century, when polka dancing was popular (hence their name), but haven't really come into fashion again except for a brief spurt of popularity in 2006.
Because of the colorful and playful nature of polka dots, polka dots are more common in women's clothing than they are in men's. However, if you want to add a touch of playfulness to your look, or want to do a throwback to earlier times, polka dots might work for you.
Like any bold pattern, polka dots are best used in moderation. It's hard to get away with wearing a polka dot shirt or pants without making a very dramatic statement:
Layering a polka dot shirt with something more conservative can be an effective combination. You can still get the effect of the polka dots, but not come off looking like a clown:
Otherwise, a touch polka dots is usually enough to get the point across: