The warp refers to the vertical array of threats through which the weft is woven. An easier way to think of this is that the weft is the continuous piece of thread that zigzags from the left to the right across the width of the fabric whereas the warp is made up of long individual threads that run perpendicular to the weft. On a loom the warp are the threads attached to the long handles often seen moving up and down crisscrossing each other while the weft is the thread on the shuttle being drawn through the crisscrossing warp.
The warp threads are held under tremendous tension when placed on a loom therefore must be quite sturdy. Traditionally wool and flax were the only two types of threat that could be used as warp due to their high strength. However with advancements in technology cotton and many man-made fibers can now be used as warp.
For the production of silk ties, both warp and weft are 100% silk. Because of the higher tension of the warp yarns, they are usually slightly thicker, and made from a higher ply silk yarn that can hold up to higher tension.