It is almost impossible to make any piece of jewelry without at least one jump ring. Jump rings are a basic building block of many types of jewelry, and are the main component when you make chain maille, a very popular style of jewelry right now.
Jump rings come in three main styles--soldered jump rings, open jump rings, and split rings.
Jump rings are made of metal wire that is made into a circle or a spring shape, then cut into a circle. Both ends should meet perfectly end to end or a jump ring is not made correctly.
An open jump ring has the cut place in the circle left open. A soldered jump ring is soldered shut at the open spot. A split ring is what you find on many key rings, a ring that is split in a tight spiral horizontally so that you can slide other rings on and off.
I like oval jump rings because the opening is on the side and keeps things more secure. Good information!