Don't confuse "ground" with dirt or water. Airplanes also have "ground" circuits. Ground, in most cases refers simply to a common point of reference. In your home (if you live in the US), your power outlets have three openings. One, the largest rectangle, is the common which carries the current returning from a properly operating device. The smaller rectangle is the hot lead, or the one that provides the power to the device. The third opening, the small D shaped opening, is a lead that ties back, ultimately to a rod driven into the earth at your service entrance. Under normal operation, this wire should carry zero current and is provided as a safety path in case something goes wrong inside a device plugged into the outlet. In most metal cased devices, the metal case is connected to a wire in the cord that connects to this pin. As oddly as it may be, the common wire and the ground wire are tied together inside the primary breaker box, which only adds to the confusion.
When a high current source gets shorted to a good ground, fuses blow, or circuit breakers pop, or wires start melting. The current is usually limited by the impedance of the current source and some small resistance that is inescapable in the ground because it is so difficult to make anything be 0.00000 ohms. Instead of seeing 100,000,000 amps flow, things usually stop at a few dozen or a few hundred amps until the wires melt.