The biretta is a square cap with three or four peaks or horns, sometimes surmounted by a tuft. Traditionally the three-peaked biretta is worn by Christian clergy, especially Roman Catholic clergy, as well as some Lutheran and Anglican clergy. A four-peaked biretta is worn as academic dress by those holding a doctoral degree from a pontifical faculty or pontifical university or faculty. Occasionally the biretta is worn by advocates in law courts, for instance the advocates in the Channel Islands.

A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 3200 BC. The origin of the word "cap" comes from the Old French word "chapeau" which means "head covering". Over time, the word has evolved and changed its meaning, but it still retains its association with headwear. Caps typically have a visor, or no brim at all. They are popular in casual and informal settings, and are seen in sports and fashion. They are typically designed for warmth, and often incorporate a visor to block sunlight from the eyes. They come in many shapes, sizes, and are of different brands. Baseball caps are one of the most common types of cap.