We’ve all heard polka music. We all wear polka dotted clothing. So what’s the connection? Why are a bunch of dots called “polka” dots? Enquiring minds want to know.

From wikipedia.org:

Polka dot is a pattern consisting of dots. Polka dot patterns are quite variable: they range from a series of dots that are equally spaced and sized to a random arrangement of multicoloured dots of different sizes. Polka dots are most commonly seen on children’s clothing, toys, and furniture, but they appear in a wide array of contexts. The pattern rarely appears in formal contexts, however, and is generally confined to more playful attire such as bathing suits. Occasionally white on black regularly spaced polka dots appear on more formal clothing.
While polka dots are ancient, they first became common on clothing in the late nineteenth century in Britain. At the same time polka music was extremely popular and the name was also applied to the pattern, despite no real connection between them.