Twill is a type of fabric woven with a pattern of diagonal parallel ribs.
It is made by passing the weft threads over one warp thread and then under two or more warp threads. Examples of twill fabric are chino, gabardine, tweed and serge.
Twill, from a practical standpoint, is a warm weather material, less well suited for cold weather.
Harris Tweed is a luxury twill handwoven on the Isle of Harris, Outer Hebrides, Scotland.