Knickerbockers are a type of men's pants, also known as trousers or breeches, that come down to the knee instead of the ankle and were especially popular in the 20th century. This type of trouser was worn in the summer by boys until they were considered adults. Once this happened, usually around puberty, boys could begin wearing regular trousers that went all the way down to the ankles. This was considered a right of passage into adulthood.
While knickerbockers were not an uncommon form of dress, the term itself came from a Washington Irving book, "A History of New York." A character in the book, Diedrich Knickerbocker, was named after a real-life man named Herman Knickerbocker. The character in the book became associated with a certain, stereotypical person who typically dresses in the knee-length trouser pants of that time. Thus the pants, and the type of person he represented, were known as knickerbockers.
This particular type of pants was known in New York where people who wore this style of pants lived. The pants become a symbol for the area, helped along by "A History of New York." Today the New York Knicks, short for the New York Knickerbockers, use the name with pride to show their state's history. It was first used to refer to Alexander Cartwright's baseball team in 1845, and since then the name has stuck. It was eventually taken on by the New York basketball team.
Today, knickerbockers are referred to as trousers and are especially popular attire for sporting events such as golfing. Golfers wear a special kind of trouser known as plus four trousers. The pants extend four inches (about 10 cm) below the knee and are more comfortable to wear while playing a game of golf. Plus twos, plus sixes, and plus eights all exist but are not as popular. Like the plus fours, each comes down a certain length below the knee as specified by the name.
Anyone who wants a pair can still find knickerbockers on sale at most clothing stores, though now they are referred to as trousers or simply capris. The term knickerbocker, while still common, is not used much in popular culture when talking about today's style of dress. Women may choose to wear this medium length style of pants, but typically the trousers are targeted at men. Women's pants of roughly the same length are usually a female type of capris, a form of knee length blue jean with a smoother, tighter appearance than men's trousers.