Within the SCA
A circlet in the SCA is a decorated metal band worn around the head. In some kingdoms, circlets are regulated with sumptuary laws, and the material and width of circlets may be restricted. For example, in some kingdoms, metal circlets are reserved for those with an Award of Arms, and in Meridies, a metal circlet wider than 1/4 inch is for people who hold a Grant of Arms. It should be noted that circlet restrictions are part of each kingdom's laws or traditions and usually not part of official SCA law.
Within the Adrian Empire
Within the Adrian Empire, a circlet is defined as "a circle of metal, no more than about a half inch or so wide. It is worn on the head, across the forehead. A circlet has smooth edges, with no decorations sticking up from the edge. These are called "points". A circlet may be plain or fancy, or even jewelled, and may be made of any metal the wearer wishes." Anyone with the title of Lord or Lady may wear a circlet. Viceroys may also choose to wear a circlet.