First, the primary job of a loom is to hold the warp threads taut. For those of you who are non-weavers, warp threads are the length-wise threads. The weft go crosswise.Unlike knitting or crocheting, in which interlocking loops form the cloth, the warp and weft cross each other at right angles. Different methods of holding the warp taut has been employed through history.
The other important feature is the ‘cross’. If one thinks about cloth, it is easy to see that the various threads don’t just lie upon one another. Each weft thread goes over and under the warp threads.Also, in a block of three weft threads, the middle one goes over and under a different warp thread. So, there must be some way of lifting the warp threads to insert each one of the weft threads. Now handweavers use a shuttle, but this is a relatively recent invention. Backstrap weavers use their fingers to lift the threads so that the finished cloth is woven in a memorized pattern. Without the cross,(I.e. where the warp threads and weft threads cross) there would be no cloth. Heddles and shed sticks (or the sheds in, say the jack loom) make it easy to lift the appropriate warp threads. Every other warp thread is lifted and then the alternate threads the next pass of the weft. This is how one ‘weaves’ the threads in and out.
Most of the other inventions connected with a loom basically provide some way to weave a pattern. Modern looms employ heddles (which look like long large eyed needles) and reeds (big comb- looking pieces).The more the slots (or dents in weaver talk) o a reed, the finer the cloth. These separate the threads and by connecting the treadles to the appropriate threads various patterns can be constructed.
As looms grew more sophisticated. they went from the basic warp and weft (2 sheds) to multiple sheds. A shed is simply the space between the warp and weft. More sheds mean more combinations for lifting the warp threads and so more patterns.