Pajamas or pyjamas, often shortened to PJs, jimmies, jimjams or jammies, can refer to several related types of clothing. Pajamas are loose-fitting garments derived from the original garment and worn chiefly for sleeping, but sometimes also for lounging, also by both sexes. More generally, pajamas may refer to several garments, for both daywear and nightwear, derived from traditional pajamas and involving variations of style and material.
The word pyjama  was borrowed c. 1800 from Urdu pāy-jāma پايجامه , itself borrowed from Persian pāy-jāmeh پايجامه lit. 'leg-garment'. The original pyjāmā are loose, lightweight trousers fitted with drawstring waistbands worn by Muslims in India and adopted by Europeans during East India Company rule in India.
The worldwide use of pajamas (the word and the garment) is the result of adoption by British colonists in India in the 18th and 19th centuries, and the British influence on the wider Western world during the Victorian era. Pajamas had been introduced to England as "lounging attire" as early as the seventeenth century, then known as mogul's breeches (Beaumont and Fletcher) but they soon fell out of fashion. The word pajama (as pai jamahs, Paee-jams and variants) is recorded in English use in the first half of the nineteenth century. They did not become a fashion in Britain and the Western world as sleeping attire for men until the Victorian period, from about 1870.
Hobson-Jobson: A Glossary of Colloquial Anglo-Indian Words and Phrases (1886) summarizes the state of usage at the time (s.v. "pyjammas"):
Such a garment is used by various persons in India e.g. by women of various classes, by Sikh men, and most by Mohammedans of both sexes. It was adopted from the Mohammedans by Europeans as an article of dishabille and of night attire, and is synonymous with Long Drawers, Shulwaurs, and Mogul-Breeches [...] It is probable that we English took the habit like a good many others from the Portuguese. Thus Pyrard (c. 1610) says, in speaking of Goa Hospital: "Ils ont force calsons sans quoy ne couchent iamais les Portugais des Indes" [...] The word is now used in London shops. A friend furnishes the following reminiscence: "The late Mr. B—, tailor in Jermyn Street, some on 40 years ago, in reply to a question why pyjammas had feet sewn on to them (as was sometimes the case with those furnished by London outfitters) answered: "I believe, Sir, it is because of the White Ants."
Traditional pajamas consist of a jacket-and-pants combination made of soft fabric, such as flannel or lightweight cotton. The jacket element usually has a placket front and its sleeves have no cuffs. Many people opt to sleep or lounge in just the pajama pants, either with a t-shirt, or, for males, barechested. For this reason, pajama pants for men and boys are often sold as separates.
Some pajamas feature a drop seat (also known as a trap door or butt flap): a buttoned opening in the seat, designed to allow the wearer to conveniently use a toilet. Drop seats were very common on pajamas made before the 1950s, but in the early twenty-first century they are rather rare.
Contemporary pajamas are derived from traditional pajamas. There are many variations in style such as short sleeve pajamas, pajama bottoms of varying length, or, on occasion, one-piece pajamas, and pajamas incorporating various materials. Chiefly in the US, stretch-knit sleep apparel with rib-knit trimmings are common. Usually worn by children, these garments often have pullover tops (if two-piece) or have zippers down the fronts (if one-piece), and may also be footed.
Although pajamas are usually distinguished from non-bifurcated sleeping garments such as nightgowns, in the US, they have sometimes included the latter as a top. Babydoll pyjamas have a kind of short dress top over shorts or short pants.
Pajamas may today refer to women's combination daywear, especially in the US where they became popular in the early twentieth century, consisting of short-sleeved or sleeveless blouses and lightweight pants. Examples of these include capri pajamas, beach pajamas, and hostess pajamas.
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Pajamas often contain visual references to a thing that may hold some special appeal to the wearer. Images of sports, animals, balloons, polka dots, flowers, stripes, plaids, foulards, paisleys and other motifs may all be used for decoration. Pajamas may also be found in plainer designs, such as plaid or plain gray, but when worn in public, they are usually designed in such a way that makes their identity unambiguous. Older styles of children's pajamas have been depicted as having a square button-up flap covering the buttocks.
Pajamas are often worn with bare feet and sometimes without underwear. They are often worn for comfort by individuals in their living quarters. Since the late 20th century, some people in Britain and the US have worn pajamas in public, whether for convenience or as a fashion statement.
In January 2012, a local Dublin branch of the Government's Department of Social Protection advised that pajamas were not regarded as appropriate attire for clients attending the office for welfare services.
In January 2012, Michael Williams, a commissioner in Caddo Parish, Louisiana, proposed an ordinance prohibiting people from wearing pajamas in public. Caddo Parish already has a law against wearing sagging pants that hung below the waist. Williams pushed for a law against pajama pants after seeing a group of young men wearing loose-fitting pajama pants that were about to show their private parts. According to Williams, "The moral fiber in our community is dwindling. If not now, when? Because it's pajama pants today, next it will be underwear tomorrow." 
Williams’ concerns are reflected in many school and work dress codes. Mount Anthony Union High School in Bennington, Vermont, banned students in 2011 from wearing pajamas to school, concerned that they could be a safety hazard.
- "'Moe' with owners James Davis & wife, in bed in children's pajamas, at home.", Life magazine, 1971, (Photographer: Ralph Crane).
- "Model clad in lounging pyjamas featuring peg-top trousers like jodpurs for sale at Neiman Marcus" Life magazine, 1939, (Photographer: Alfred Eisenstaedt)
- "Brazilian composer Heitor Villa-Lobos playing native Brazilian folk instrument from his collection, while wearing jacket over his pajamas & smoking cigarette; at home." Life magazine, 1945 (Photographer: Unknown; Location: Rio De Janeiro)
- Oxford English Dictionary 3rd edition, December 2007, s.v.
- Omoniyi, Tope (2016), The Cultures of Economic Migration: International Perspectives, Routledge, p. 228, ISBN 978-1-317-03654-8,
But under Muslim rule (in India) ... a variety of sown clothes started emerging .... Muslims introduced pyjamas and kurtas
- Lewis, Ivor. 1991. Sahibs, Nabobs and Boxwallahs: A Dictionary of Words of Anglo-India. Oxford: Oxford University Press. 266 pages. ISBN 0-19-564223-6. "They were introduced in England as lounging attire in the 17th century but soon went out of fashion. About 1870 they reappeared in the Western world as sleeping attire for men, after returning British colonials brought (them) back ...." Encyclopædia Britannica. Retrieved December 29, 2006, from: Encyclopædia Britannica Online.
- Yule, Henry and A.C. Burnell, Hobson-Jobson: A Glossary of Colloquial Anglo-Indian Words and Phrases (1886), s.v. Pyjammas, p. 748. Hobson-Jobson glosses "white ants" as "The insect (Termes bellicosus of naturalists) not properly an ant, of whose destructive powers there are in India so many disagreeable experiences, and so many marvellous stories."
- "Girl sitting on bed and wearing striped flannel pajamas and Donald Duck slippers." Life magazine, December 1949, (Photographer: Nina Leen).
- "Millionaire Charles Ponzi posing for photograph in pyjamas." Life magazine, 1942, (Photographer: Hart Preston).
- "Three college students wearing their PJs and playing in the bunk bed of their dorm room during rush week at the University of Illinois", Life magazine, September 1956 (Photographer: Grey Villet).
- "Model wearing cotton-crepe pyjamas." Life magazine, 1939, (Photographer: Alfred Eisenstaedt).
- "Harriet Traynham (R) and her guests still wearing their pyjamas at 3:15 pm," Life magazine, August 1951 (Photographer: Lisa Larsen)
- "Actress Dorothy McGuire doing morning exercises wearing silk pajamas." Life magazine, 1941, (Photographer: Alfred Eisenstaedt)
- "Cynthia Brooks standing with her mother who is making alterations on her 'baby doll' pajamas", Life magazine, March 1957, (Photographer: Peter Stackpole)
- "Czech model posing in hostess pajamas." Life magazine, 1968, (Photographer: Bill Ray)
- "Now they're shopping in pyjamas in Shanghai!" Liverpool Echo, 17 January 2009. Retrieved 1 May 2015.
- Helen Pidd. "Tesco bans shopping for bananas in pyjamas ... or bare feet". the Guardian.
- "BBC NEWS - Middle East - Pyjama ban for UAE civil servants".
- "Tesco ban on shoppers in pyjamas". BBC News. 2010-01-28. Retrieved 2013-01-23.
- "Meanwhile, In Blanchardstown". Broadsheet.ie. 2012-01-24. Retrieved 2013-01-23.
- "Louisiana Official Moves to Ban Wearing Pyjamas in Public" Courtney Subramanian. Retrieved April 15, 2012
- "Pyjamas in Public a Real Crime? | NBC 5 Dallas-Fort Worth". Nbcdfw.com. 2012-01-17. Retrieved 2013-01-23.
- "Vt. high school dress code now bans pyjamas" Retrieved on April 15, 2012