A lightsaber is an energy blade originating from the movies/books/series known worldwide as STAR WARS. The idea for Star Wars was originally George Lucas', but many people have added stories and details into the rich world of Star Wars. Exar Kun, a Jedi Knight-turned-Dark Lord of the Sith, built a lightstaff, or dual-emitter-lightsaber. He modified his lightsaber, adding a second emitter matrix to the butt of his lightsaber, enabling him to weild the 'saber like a quarterstaff. In the movie Star Wars Episode I: The Phantom Menace, Darth Maul fights Obi-Wan Kenobi and Qui-Gon Jinn using a similar lightstaff.
If you wish, /msg WonkoTheSane and I'll add another writeup dealing with lightstaves.

Among the Old Republic's many legends, none endure more than the stories of the Jedi Knights and their incredible lightsabers.

A lightsaber's handgrip is usually twenty-four to thirty centimeters long and features a mirrorlike concave metal disk, known as a blade emitter, at one end. Controls include an activation lever, a recharge socket, diagnostic readouts, and in some of the weapons, blade length/intensity controls. Opening the small access panel reveals a tiny but very sophisticated power cell as well as at least one - and sometimes many - high quality, multifaceted jewels.

A lightsaber's jewel(s) focus the power cell's energy charge into a tight parallel beam that emerges from the blade emitter as a vibrant blade of pure energy. The blade is a closed energy loop. It's amplitude determines when the energy beam arcs back to the negatively charged high-energy flux aperature that rings the outer edge of the lightsabre's concave disk. The power cell can last for years because it is fed by the energy that enters the flux aperature; the weapon loses energy only when it makes contact with another object.

The lightsaber's deadly energy blade can cut through almost any substance. Because the blade itself has no weight and emits no heat, a novice may easily miscalculate its path. A Jedi Knight undertakes years of study to master the weapon, developing the skill that allows him or her to block incoming blaster bolts or fend of more than a dozen attackers.

Each lightsaber is custom built, normally by the Jedi student as one of the tests of an appretice's skills. After his disasterous defeat at Cloud City, Luke Skywalker retired to Obi-Wan Kenobi's hut on Tatooine to build his new lightsabre, perhaps hoping that the familiar and comfortable place would provide solace as he grappled with the knowledge that Darth Vader might be his father.

Lightsabers are also known to make a distinctive buzzing sound when swung through the air, no matter what the speed of the blade. When two lightsabers collide, a great amount of energy is released, putting a great strain on the power packs, as the lightsabers attempt to cut through each other. A sharp, hissing, electric clap is emitted, in addition to a flash of light, when the energy blades of different lightsabres collide. Although no heat is radiated beyond the light shaft, a wound from a lightsabre is instantly cauterized by the great heat. Qui-Gon Jinn used the heat energy potential of his lightsabre to melt a door down in The Phantom Menace.

Most lightsabers have customized features such as pressure-sensitive activation levers (the blade will disappear after the user lets it go, and simply holding the lightsabre will activate the blade: no need to fiddle with a switch) and multiple crystals that enable the user to alter the amplitude and length of the blade. The lightsabre's handgrip is as much a work of art as a practical weapon, often featuring a design native to the Jedi's homeworld or built by the student in a style reminiscent of his master's lightsabre.

The Jedi drew their lightsabers only as a last resort - when negotiations failed to resolve a dispute peacefully - but their skills were unquestioned once these magnificent energy blades flashed. The Empire nearly succeeded in exterminating the Jedi, but Luke Skywalker has been training a new generation of Jedi Knights, who proudly wield their lightsabers in defense of the New Republic, reaffirming traditions of courage and honor that have endured for a thousand generations.

Thanks to George Lucas for having a good idea, and to everyone at E2 for making this site awesome. This information was stolen from cited from STAR WARS: The Essential Guide to Weapons and Technology by Bill Smith.