I am weaving twill these days. It is called vaðmál in Icelandic. The English term is vadmal.
These terms indicate that the lines that the warp and weft form are diagonal and there are various angles of lines that make different forms of twill : 14°,18°, 27°, 45° and 63°.
The different forms of twill have an array of names: herringbone, goose eye, overcheck herringbone, barleycorn, houndstooth, broken twill. plain twill, glen check, gun club check, broken twill and tattersall. Probably there are more terms.
The one I am weaving is a weft faced herringbone, at 45°.
Of course it is made from RAGS! ;)
Anna María Lind, MA Textile Art from Winchester School of Art.