Knickers is a word used to refer to two very different items of clothing.
As an abbreviation for knickerbockers, it is a term for mens' or boys' baggy knee trousers, of a type particularly popular in the early 20th century. Golfers' plus twos and plus fours, now also generally a thing of the past, are trousers of this type.
Otherwise, and especially in Britain, it is a term for panties or similar women's undergarments.
