In the English speaking world, in particular United Kingdom, Ireland, some Commonwealth countries, and occasionally in United States, knickers is a word that is used to describe women's and occasionally (but quite rarely) men's underpants and undergarments, women's lingerie, and for sports pants sportswear. In the United States it more commonly used as a short form for Knickerbockers, a type of golfing pants, also called Plus fours.

The word carries a naughty or playful connotation, which keeps it in use in the media. The word has entered the English language in many ways. The phrase 'Knickers to you' has evolved into a favourite way of telling someone that one doesn't care about them or their opinion. The phrase 'Don't get your Knickers in a twist' is in common usage, as a way of telling someone to 'calm down' and 'don't get angry'. The phrase 'Fur coat and no knickers' describes a woman who looks rich and glamorous, but is in fact not so classy. 'Oh Knickers' is a favourite expletive, which is used when something has gone wrong. French knickers describe a loose fitting boxer like underpants, which may be made of silk or satin, typically with a lace trim.

In older usage knickers referred to men's garments such as knickerbockers, also known as plus twos or plus fours in British English. The term knickerbockers has become historic in British English but is used in North America. The term "knickers" is still used to refer to knickerbockers in American English. However, the adoption of the term "knickers" to denote a women's undergarment in British English has caused the expression, along with "knickerbockers" to become historic.

George Cruikshank, whose illustrations are classic icons for Charles Dickens's works, also did the illustrations for Washington Irving's droll History of New York (published in 1809) when it was published in London. He showed the old-time Knickerbockers, Irving's fictitious Dutch colonial family, in their loose knee-length Dutch breeches. By 1859 relatively short loose ladies' undergarments, a kind of abbreviated version of pantalettes or pantaloons, were known as "knickers" in England, but this is often used as a general term for all women's underwear. There are now many names for women's undergarments that are sometimes called knickers, such as panties, thongs, g-strings, briefs, shorts, tangas and others.

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French Knickers are a type of lingerie and are sometimes called "tap pants", i.e. tap-dancing pants. The term is predominantly used in the UK to describe a type of underwear worn from the hip. They cover the hip, most of the upper thigh and all of the buttocks, and are denominated by the 'open leg' style, or loose fitting leg. They do not have elasticated leg cuffs, but allow a pleated, more comfortable fit. The style may have straight cut leg cuffs with or without trimming, or the leg cuffs may be bias cut to a degree.

They are not to be confused with "hipsters' or "briefs", or "bikini bottoms" and "boyshorts", all of which feature elasticated leg openings and much snugger fit to the body.

The french knickers should only be worn with A-Line type skirts and free-flowing dresses, which require freedom of movement without the visible panty line (VPL), because the french knickers would give a smooth appearance underneath the fabric of the clothing aforementioned, therefore suitable for day wear or evening outfits for this reason.

History of French Knickers