Roving is wool that has been run thru a mill on a carding machine. A carding machine has many teeth that brush the fiber (like a giant hairbrush) into generally the same direction. When you spin roving into yarn, it’s called woolen style yarn (or simply “woolen” even if it’s not made out of wool). Roving is also a great fiber for felting, as the fibers are not all in alignment and can grab onto each other easily during the felting process.