The fundamental structure of a rug is a series of interwoven strings called warps and wefts.
These are mostly made from cotton, wool or silk (Some warps are made of animal hair depending on the region). Looking straight at a loom, the strings that go up and down vertically are called warps. Warps also will eventually end up as the decorative fringes at either end of the rug. The material that goes back and forth horizontally is called the weft.
The interlocking of the warp and the weft create a simple structure not unlike burlap. Simply put, an oriental rug takes this structure and adds decorative knots between each row of wefts. The knots are woven around two warps.
Below is a picture of an oriental rug stripped of all its knots except for four. The picture shows two different weaving styles:
Below, a close up of the previous picture demonstrates a weave using only one weft, similar to a traditional burlap.
Pictured below is the close up of a two-weft weave. The second weft provides additional security in locking each knot in place. This will be explored later in detail.