A clerical collar is a piece of clerical clothing. It is a detachable collar that buttons onto a clergy shirt or rabbat (vest), being fastened by two metal studs, one attached at the front and one at the back to hold the collar to the shirt. The collar closes at the back of the neck, presenting a seamless front. It is almost always white; and was originally made with cotton or linen but is usually made with plastic now. Sometimes (especially in Roman Catholic practice) it is attached with a "collaret" or "collarino" that covers the white collar almost completely, except for the top edge and a small white square at the base of the throat, to mimick the collar of a cassock. Sometimes the collar is black (or whatever color is appropriate to the rank of the clergyman), with only a detachable tab of white in the front.
The clerical collar is a fairly modern invention (the detachable collar itself is supposed to have been invented in 1827), although the "collarino" may date as far back as the 17th century. The Church of England's Enquiry Centre reports (citing the Glasgow Herald of December 6, 1894) that the practice of Anglican clergy wearing a detachable clerical collar was invented by a Rev Dr Donald McLeod and became more popular through the Oxford Movement.
In the Roman Catholic Church, the clerical collar is worn by all ranks of clergy, thus, bishops, priests, and deacons—normally transitional but occasionally permanent; often by seminarians who have been admitted to candidacy for the priesthood, as is the case in the Diocese of Rome; and by college and graduate level seminarians with their cassock during liturgical celebrations.
In the Eastern tradition, amongst Catholic and Orthodox easterners, a band collarette with no "notch" in front may be worn by seminarians, although the norm is still a standard clerical collar. However, as the cassock is more commonly, if not mandatorily, worn to classes, often a plain white shirt will suffice, or a band collar with no collarette. Slavic cassocks button to the side, and thus a collar is often pointless, whereas a Greek cassock buttons to the front and has a higher collar, so the collar prevents chafing - as was its original function under a cassock. Eastern deacons and sometimes subdeacons, but rarely readers or clerics, also wear a clerical collar, with subdeacons and readers often having a style with no notch, or a tab shirt with no tab.
Collars are typically worn by clergy members of other Christian Churches such as Anglican, Presbyterian (the clergy collar is said to have originated in Scotland) and Lutheran Churches. Also many Methodist, Apostolic, Oneness Pentecostals, Non-denominational, and other Christian ministers wear collars. Some Unitarian Universalist ministers--Humanists as well as Christians--wear collars. In some churches or locales this practice is discouraged because collars are assumed to be associated with Roman Catholicism.
In the United Kingdom and the United States, clerical collars are sometimes informally called dog collars. The term "Roman collar" refers to a style and does not necessarily mean that the wearer is Roman Catholic.