A biretta is a traditional square cap worn by members of the clergy in the Roman Catholic Church and some other Christian denominations. It is typically worn during liturgical ceremonies, such as Mass or the Liturgy of the Hours, and is a symbol of the wearer's academic degree and clerical rank.

The biretta is indeed a distinctive cap worn by members of the clergy in the Roman Catholic Church and certain other Christian denominations. Here are some key features and details about the biretta:

1. **Design:** The biretta has a square shape with three or four peaks or horns. It is often made of stiffened fabric or covered cardboard.

2. **Color:** The color of the biretta can indicate the wearer's clerical rank. For example, a black biretta is commonly worn by priests, while bishops and cardinals may wear a purple or red biretta.

3. **Pompom or Tassel:** At the center of the biretta's crown, there is usually a pompom or tassel. The color of the pompom or tassel can also carry significance, with black, purple, red, or other colors denoting different ranks.

4. **Liturgical Use:** The biretta is typically worn during specific liturgical ceremonies, such as processions, Mass, or other formal occasions. It is often removed during prayers or while seated.

5. **Academic Significance:** In addition to its liturgical use, the biretta is a symbol of the wearer's academic degree. Different peaks may represent different degrees, and the biretta is sometimes worn in academic processions.

While the use of the biretta is most associated with the Roman Catholic Church, variations of this cap can also be found in Anglican, Lutheran, and some other Christian traditions.