In the Star Wars series, a Jedi is a Force-user aligned with the light side. The Force is a life-force that binds the universe together and may be used to change events in the world at large, by manipulating the underlying nature of life. In Star Wars, the great power that this entails has divided Force-users diametrically: those who favor its use for good align with the Light, while those that seek to use their force powers for personal gain, inevitably are tempted by this slight variance to fall utterly to the Dark side. To walk in the Light, as a Jedi, is a strict way of life, and so is a challenge for those in the Star Wars universe to live up to.
Jedi use "lightsabers," or swords emitting beams of pure light, to deflect energy weapon fire and as an offensive weapon. The lightsaber is a symbol of peace and refinement, according to Obi-Wan Kenobi, less casual and haphazard than traditional weapons, and implying a commitment to the finesse and perfect of form required by duelists and light Jedi alike.
Effects on the Real World
The Jedi Way is a fictional religion/philosophy from the Star Wars movie series. In a recent census in Australia, pranksters claimed "Jedi" as their religion in hope of getting it recognized as a legitimate faith.