Wren day also known as Wren's day, Hunt the Wren Day or The Hunting of the Wrens (Irish: Lá an Dreoilín) celebrated on 26 December, St. Stephen's Day. The tradition consists of "hunting" a fake wren, and putting it on top of a decorated pole. Then the crowds of mummers or strawboys celebrate the Wren (also pronounced as the Wran)^{[citation needed]} by dressing up in masks, straw suits and colourful motley clothing and, accompanied by traditional céilí music bands, parade through the towns and villages. These crowds are sometimes called wrenboys.

In past times, an actual bird was hunted by Wrenboys on St. Stephen's Day. The captured wren was tied to the Wrenboy leader's staff pole. The captured wren would be kept alive as the popular mummers' parade song states 'A penny or tuppence would do it no harm'. The song, of which there are many variations, asked for donations from the townspeople. Often, the boys gave a feather from the bird to patrons for good luck. The money was used to host a dance for the town, held that night. The pole, decorated with ribbons, wreaths and flowers, as well as the Wren, was the centre of the dance. Over time, the live bird was replaced with a fake one that is hidden, rather than chased. The band of young boys has expanded to include girls, and adults often join in. The money that is collected from the townspeople is usually donated to a school or charity. A celebration is still held around the decorated pole.

The wrens are passerine birds in the mainly New World family Troglodytidae. There are approximately 80 species of true wrens in approximately 20 genera. The genus eponymous of the family is Troglodytes. Only the Eurasian Wren occurs in the Old World, where in Anglophone regions it is commonly known simply as the "wren" as it is the originator of the name. The name wren has been applied to other unrelated birds, particularly the New Zealand wrens (Acanthisittidae) and the Australian wrens (Maluridae).

Most wrens are small and rather inconspicuous, except for their loud and often complex songs. Notable exceptions are the relatively large members of the genus Campylorhynchus, which can be quite bold in their behavior. Wrens have short wings that are barred in most species, and they often hold their tails upright. As far as known, wrens are primarily insectivorous, eating insects, spiders and other small arthropods, but many species also eat vegetable matter and some will take small frogs/lizards.

A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun, also known as daytime. The period of time measured from local noon to the following local noon is called a solar day.

Several definitions of this universal human concept are used according to context, need and convenience. In 1967, the second was redefined in terms of the wavelength of light, and it became the SI base unit of time. The unit of measurement for time called "day", redefined in 1967 as 86,400 SI seconds and symbolized d, is not an SI unit, but it is accepted for use with SI. A civil day is usually also 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time UTC, and, in some locations, occasionally plus or minus an hour when changing from or to daylight saving time. The word day may also refer to a day of the week or to a calendar date, as in answer to the question "On which day?" Day also refers to the part of the day that is not night — also known as 'daytime'. The life patterns of humans and many other species are related to Earth's solar day and the cycle of day and night (see circadian rhythms).