The shuffle is a basic pattern for juggling multiple diabolos. The diabolos are pushed off the string from one side of the pattern so they go over the other diabolos, then caught on the string on the other side and pushed back over to the throwing side of the string, so they go around in a low circle.
Another way to juggle multiple diabolos besides the shuffle is in a high pattern, where the diabolos are thrown higher, one at a time, and there is never more than one on the string at once, as opposed to the low pattern (the shuffle), where there can be more than one diabolo on the string at the same time. 5 is the highest number of diabolos that have been qualified in the low pattern, and 6 is the highest number that have been done for at least a flash.