Open Culture:

For the uninitiated, the warp are the plain vertical threads of a weaving or tapestry, through which the colorful, horizontal weft threads are passed, over and under, on wooden needle-shaped bobbins (or shuttles).

As in the 17th-century, giant looms are strung with white warp threads, in readiness for the threads expert dyers have colored according to the artist’s palette.

This is an amazing video. I’ve seen these kinds of tapestries when I traveled in Europe and always wondered how they were created.