What does X-Dyed Fabrics mean?

Cross dyeing is a technique used to dye material made from more than one type of fiber.

Heddels explains X-Dyed Fabrics

During the process, the fabric is dipped into several different dye baths. Each fiber type will only absorb the dyes to which it has an affinity. The end result is a cross-dyed fabric with a lovely, multi-toned heather appearance.

Additional Resources

Here is an example of x-dyed fabrics: