Weaving involves interlacing two sets of strings at right angles to form a mesh. The machine on which cloth was woven was a loom. All that a loom does is hold one set of strings tight so that a second set can be fed through the first to make a weave. The tight set of strings is called the warp. The second, “active” set is called the weft—which is simply an old form of the verb weave.
