What is a pork pie hat?

A pork pie hat is a low, round-crowned hat with a slightly upturned brim. It was popularised in the early 1800s when pork pie bakers created the hat as a way of advertising their pies – they wore the hats and carried the pies on trays or in baskets balanced on top. The hats are popular fashion items and often associated with jazz musicians and gangsters of the 1920s.