A tiara is a jeweled head ornament that is worn by women at formal occasions. It is a semicircular headpiece that is usually made of silver, gold, or platinum and decorated with precious stones, pearls, or cameos. Tiaras were first worn in ancient Iran and were later adapted by Greco-Romans. They became popular in Europe in the late 18th century as a prestigious piece of jewelry to be worn by women at formal occasions. Tiaras were extremely popular during the late 19th century and were worn at events where the dress code was white tie. After World War I, wearing a tiara gradually fell out of fashion, except for official occasions at a royal court. However, interest in tiaras has increased again since the beginning of the 21st century.

Tiaras are usually richly decorated with precious stones, pearls, or cameos, often arranged in symmetrical patterns. Common elements in these patterns are arcs, garlands, circles, stars, and stylized flowers or leaves. Occasionally, flowers, ears of corn, dragonflies, or butterflies are depicted more or less true to life by using gemstones in different colors. Tiaras can also be made from unusual materials such as tortoiseshell, coral, quartz, horn, and aluminum.

The word "tiara" is often used interchangeably with the word "diadem". Nowadays, tiaras are not only worn by queens and princesses but also by winners of beauty contests, girls for various events like gala, and brides on their wedding day.