DowsingDowsing is loosely defined as the ability to detect flowing underground water, without using the expected tools, i.e. a shovel. People who use this method swear by it, while people who don't tend to swear about it.
In its most common form, a dowsing rod is used. There are two types of dowsing rods, Y- and L- shaped. The Y shape is held on top of the hands so it aims forward, while two L-shaped rods are held out aimed away from each other. If you pass over running water, the rods will turn to reflect this.
Does this work? Well, don't ask us, we drink from the tap. But folks who needed to find water on the property think it's the real deal. The common question would be to ask how much money could be made from it if it's a fraud; and with classes to learn how to dowse going for $50 and rods selling for close to that, our eyebrows raise a bit.
Naturally, it is thought that dowsing can be used to find things other than water, for example, you guessed it, Gold. All the good magic powers involve gold, so that's an excellent sign as well. There are also other tools besides rods that can be used, including pendulums and "bobbers", which presents more things to purchase. Don't worry, you're sure to find the one that works for you, and a number of Dowsing organizations exist to help you along. To their credit, most of the information they could possibly sell you are available on their websites at no cost.
If you stray too far in any direction from the someone plausible and understandable core of dowsing, you start finding yourself in serious literature littered with terms like Geomancy, Labyrinths, Ley Lines, Feng-Shui and then it pretty much all goes to hell. This is the case with many supernatural arts where some aspects of it appear not to be explained; every other nutjob with an unexplained talent (or a pamphlet about it) shows up to the convention.