A shirt stud is a decorative fastener

Fastener

A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...

 that fits onto a buttonhole

Buttonhole

Buttonholes are holes in fabric which allow buttons to pass through, securing one piece of the fabric to another. The raw edges of a buttonhole are usually finished with stitching. This may be done either by hand or by a sewing machine. Some forms of button, such as a Mandarin button, use a loop...

 on the front of a pleat

Pleat

A pleat is a type of fold formed by doubling fabric back upon itself and securing it in place. It is commonly used in clothing and upholstery to gather a wide piece of fabric to a narrower circumference....

ed shirt

Shirt

A shirt is a cloth garment for the upper body. Originally an undergarment worn exclusively by men, it has become, in American English, a catch-all term for almost any garment other than outerwear such as sweaters, coats, jackets, or undergarments such as bras, vests or base layers...

, or onto the starched bib of a stiff-front shirt. Such shirts have special buttonholes solely for shirt studs.

A shirt stud may be fashioned from alloys, precious metal

Precious metal

A precious metal is a rare, naturally occurring metallic chemical element of high economic value.Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals...

s, and gemstone

Gemstone

A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...

s—materials uncommon to button

Button

In modern clothing and fashion design, a button is a small fastener, most commonly made of plastic, but also frequently of seashell, which secures two pieces of fabric together. In archaeology, a button can be a significant artifact. In the applied arts and in craft, a button can be an example of...

s sewn on shirts. The stud may have an inlay

Inlay

Inlay is a decorative technique of inserting pieces of contrasting, often coloured materials into depressions in a base object to form patterns or pictures that normally are flush with the matrix. In a wood matrix, inlays commonly use wood veneers, but other materials like shells, mother-of-pearl,...

, such as of pearl

Pearl

A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...

 or onyx

Onyx

Onyx is a banded variety of chalcedony. The colors of its bands range from white to almost every color . Commonly, specimens of onyx contain bands of black and/or white.-Etymology:...

.

Dress code of the modern western world

Dress code (Western)

A dress code is a set of rules governing what garments may be worn together and in what setting. Examples of dress codes are combinations such as "smart casual", or "morning dress". A classification of these codes is normally made for varying levels of formality and times of day...

 reserves shirt studs for men's formal wear

Formal wear

Formal wear and formal dress are the general terms for clothing suitable for formal social events, such as a wedding, formal garden party or dinner, débutante cotillion, dance, or race...

 and some semi-formal

Semi-formal

In Western clothing semi-formal is a grouping of dress codes, indicating the sort of clothes worn to events with a level of protocol between informal and formal...

 occasions.

In the western world

Western world

The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

, shirt studs were first used in the mid-19th century, when some shirt fronts were too stiff to close with buttons. So remains the case for the heavily starched, modern full dress shirts worn with white tie

White tie

White tie is the most formal evening dress code in Western fashion. It is worn to ceremonial occasions such as state dinners in some countries, as well as to very formal balls and evening weddings...

.