Wormrider refers to those who mastered the skill of calling, climbing, and riding a Sandworm of Arrakis.
The name referred also to the followers of the original wormrider, Selim Wormrider. They were the precursors of the Fremen. The Wormriders were Buddislamics who revered Shai-Hulud as a manifestation of Buddallah. They shared Selim's vision and ideals and were tasked to disrupt the commercialization of Spice.