Noun
a stiff white collar with no opening in the front; a distinctive symbol of the clergy
Source: WordNetThe most known form of distinctive clothing for the priest is the easily identifiable clerical collar (or Roman collar ), which takes form in either the traditional cassock, or modern day clerical shirt. Source: Internet
In certain jurisdtictions in North America and Western Europe, a Roman collar is often worn, although this is not a traditional or widespread practice. Source: Internet
The decision as to whether deacons wear the Roman collar as street attire is left to the discretion of each bishop for his own diocese. Source: Internet