Tartan is made with alternating bands of coloured (pre-dyed) threads woven as both warp and weft at right angles to each other. The weft is woven in a simple twill, two over—two under the warp, advancing one thread at each pass. This forms visible diagonal lines where different colours cross, which give the appearance of new colours blended from the original ones. The resulting blocks of colour repeat vertically and horizontally in a distinctive pattern of squares and lines known as a "sett". Tartan is often called "plaid" (particularly in North America), but in Scotland, a "plaid" is a large piece of tartan cloth, worn as a type of kilt or large shawl. The term "plaid" is also used in Scotland for an ordinary blanket such as one would have on a bed.