Setting is the metal that holds the stone in a piece of jewelry. Most of us think of rings when we think of a setting, but it can be anything affixed to metal. Another term for setting you find occasionally is mount.
Two of the most popular settings are bezel and prong, and most of the jewelry you find today has a variation on one of these. Most typical engagement rings use a type of prong setting, while other types of jewelry use a bezel set more often. These are generalizations, of course, and you can find either setting on any piece of jewelry.
Prong settings have the advantage of showing off more of the stone. This can be a disadvantage because you will need a nicer stone or you are more likely to notice inclusions on the side. There is also less material around the stone to protect and hold it in place, so a prong setting requires more periodic maintenance and inspection.
Bezel settings are the earliest form of setting where the most of the stone is surrounded with the metal. This type of setting is popular in handmade jewelry due to its durability and variety. Because the stone is protected with the metal it is a very functional setting. You will still need to have your stone inspected, just far less often and with usually minimal repairs. The disadvantage of a bezel is that you see less of the stone. Varieties of bezel setting include a half bezel, full bezel, and decorated bezel.
Decorated bezel is simply a bezel that has any sort of design in the metal.
Knowing the difference between the different settings can help you make a more informed decision with your jewelry. Keep a bezel open as an option if you decide on a custom engagement ring. It is an understated, hand made look that is durable and easy to wear.