Definition: Training lightsabers are lightsabers used by Jedi or Sith trainees to practice fighting techniques. Lightsabers are dangerous weapons -- have you noticed that someone loses a limb to a lightsaber in every Star Wars film except The Phantom Menace? At least one Jedi trainee, Tenel Ka Djo (in the Young Jedi Knights series), has lost a limb in a lightsaber training accident. Training lightsabers are very important for keeping Force-sensitive children safe from these kinds of injuries.
In-universe: The blade of a Jedi training lightsaber is shielded by a powerful electromagnetic field. At worst, a hit from a training lightsaber will produce a painful burn. Though this doesn't permanently harm a Jedi trainee, it helps him learn the importance of avoiding attacks in the future.
The shielded training lightsaber was primarily used in the Jedi Temple during the time of the Republic. After the Jedi Purge, the knowledge of how to make these training lightsabers was temporarily lost. Students in the New Jedi Order practiced with wooden training swords.
The Sith in the Old Republic used a training lightsaber with a durasteel blade covered with the toxic barbs of the pelko bug. A hit from the weapon causes temporary paralysis, simulating the effects of a lightsaber injury.
- Jedi vs. Sith: The Essential Guide to the Force by Ryder Windham (Del Rey, 2007)
- Darth Bane: Path of Destruction, by Drew Karpyshyn (Del Rey, 2006)