Coarse jute or hemp woven in a basket weave. In Great Britain, where basket weave is called hopsack weave, the fabric was originally used for bagging hops.
Rough basket weave fabric of wool can be called hopsacking, as can fabrics of various fibers that look like hopsacking.
Uses for jute and hemp hopsacking: Bags for commodities, interior decoration
Uses for wool and other fibers: Apparel
See also:
Burlap
Monk’s cloth