That would be a "Celtic Cross". Copied & pasted info below.
The Celtic cross is a symbol used today in many contexts, both religious and secular. The Celtic cross is like a traditional cross but with a ring around the intersection of the stem and arms. The whole cross is often decorated with ornate Gaelic patterns. Sometimes the Celtic cross is set on a tall base to resemble more closely the traditional Christian cross, and at other times the symbol stands alone. The Celtic cross is sometimes nothing more than a simple “stick” drawing on a gravestone or at a religious site; other times it is sculpted and quite ornate. The Celtic cross is also called the “sun cross” by some who interpret the ring to represent the sun.