A split ring is a ring you make in tatting when you want rings to be concurrent, one after the other, next to each other in a row without any chains joining them.
Using split rings, the tatter does not need a chain to move between rings. Using split rings, you can also produce a ring with two colors.
Two shuttles are required for split rings.
In basic terms, a split ring is made by starting out the way you normally would start out when doing a ring, by wrapping the core thread all the way around your hand and then using the working thread to start a ring.
The first half of the ring is made as you normally would make a ring, by doing the required number of double stitches and including the flip in your tatting motions for both halves of all double stitches.
The second half of a split ring is done by reversing and doing the second half of a double stitch, followed by doing the first half of the double stitch. However, the second half of a split ring involves NOT doing the flip for any of the double stitches.