Pajamas are articles of clothing worn to bed when it is time to sleep. Pajamas are usually referred to in the plural form due to the fact that pajamas worn by adults are typically made up of two articles of clothing; both the top and bottom which oftentimes coming in a matched pair. The shorthand term PJ’s is often used when referring to pajamas.
Pajamas for young children and toddlers typically take the form of a single article of clothing that covers the entire body and is closed at the front with a full-length zipper. These are commonly referred to as onesies.
Originally pajama referred to a lightweight, loose fitting trouser that closed with a drawstring at the waist. These pajamas originated in South and West Asia and were worn by both men and women. It is easy to see the relationship between modern-day pajamas and the original pants for which the term was coined. While pajamas were once very popular prior to the 1990s they have since become slightly less popular in western countries with many people choosing to sleep in their undergarments or a T-shirt instead of a pair of pajamas; although when using the term loosely to define any article of clothing worn to bed almost anything can be classified as pajamas.