Final answer:
Knickerbockers are trousers that were popular in the early 20th century, known for their loose fit and bunching at the knee. The term originated from the fictional character Diedrich Knickerbocker and became associated with New York culture.
Step-by-step explanation:
Knickerbockers, often simply called knickers, are a style of trousers that were popular in the early 20th century. They are characterized by their loose fit and by being bunched around the knee, where they are fastened. This knee-length style provided ease of movement compared to the full-length trousers of the time, which made them especially popular for sports like golf and for boys' school uniforms.
The term knickerbockers is derived from the fictional character Diedrich Knickerbocker, who was depicted in Washington Irving's 1809 book 'A History of New York' wearing pants of this style. Over time, the character's last name became associated with not just this style of pants, but also with New York culture in general. The term is still referenced today, notably with the New York Knicks, a professional basketball team which derives its name from this piece of sartorial history.