Force barrier or Force (war) shield was both an offensive and defensive Force power, aligned neither with the light or dark sides of the Force, that created a barrier or wall of Force energy around the intended target, be it self, friend, or foe.
Force barrier was a very basic application of the Force. Depending on the individual, it manifested itself differently, appearing as a shimmering, stasis field of Force energy, or sometimes not "appearing" at all. In combat, these barriers were capable of absorbing a wide variety of physical, energy or melee-based attacks. More adept users could employ Force barriers offensively, creating the same "wall" around an assailant and effectively preventing them from commencing an attack. Depending on the strength of the individual, the barrier could only withstand a few attacks before collapsing. There have been some cases where a barrier has repelled high and low pitched sound. Obi-wan Kenobi used this technique when a bounty hunter was firing at him with a sonic boom grenade launcher.
First practiced by the Umbaran Shadow Assassins, the technique was later adopted by both Jedi and Sith. Masters would train their pupils to use Force barriers instinctively to the point of becoming a matter of reflex. As early as 4,000 BBY, Jedi Masters prepared their students by teaching them to master Force barrier before sending them into battle. One such example was Master Arca Jeth, who, among other things, taught his three apprentices to instinctively create Force shields. Jedi apprentices on the ancient library world of Ossus also learned Force shielding before going into battle. During the New Sith Wars, students of the Sith Academy on Korriban learned to implement Force barrier as second nature, practicing it alongside their lightsaber skills in the Academy's dueling ring. In Luke Skywalker's New Jedi Order, children were taught to protect themselves with shimmering Force barriers when they first began to recognize the power of the Force. At just five years old, Skywalker's twin neice and nephew, Jacen and Jaina Solo were proficient in creating Force barriers, having learned directly from their uncle.
While training with Thon on the planet Ambria, Nomi Sunrider, her daughter Vima, and Thon were attacked by Bogga the Hutt's gang of pirates. When the thugs fired upon Thon and his apprentices from their hovercraft, the Jedi Master was able to use the Force and deflect the incoming salvos. Later, when the gang surrounded and seemingly captured the Jedi trio, Thon again used the Force as a shield to repel the incoming attacks. The pirate Gudb described Thon's shield as being strong enough to halt the advance of a sandcrawler.
During the Freedon Nadd Uprising, Jedi Knights Dace Diath, Nomi Sunrider, Kith Kark, and Shoaneb Culu used the Force collectively to create a defensive war-shield of protection against the attacking Naddists. The Force barrier they created was not visible, but it was successful in repelling the onslaught of attacks the Jedi faced as they charged forward.
During the Duel on Tython, Jedi Lord Valenthyne Farfalla used Force barrier both offensively and defensively against Darth Bane. As fellow Jedi Master Raskta Lsu dueled with Bane, Farfalla shielded Lsu from Bane's dark side onslaught with a Force barrier. When the Dark Lord tried to rush Worror (who was providing a source of empowerment to the Jedi through his battle meditation), Farfalla again threw up a Force barrier around Bane to halt his attack. Farfalla gathered energy from the light side of the Force, and at the last moment released it in a single concentrated burst of energy, encasing Bane in a stasis field of light side power. This was not enough to subdue a Dark Lord of the Sith however. The shield exploded into energy fragments as Darth Bane broke free.
After being kidnapped by Lord Hethrir, five year olds Jacen and Jaina Solo attempted to shield themselves and their brother Anakin with a shimmering Force barrier. Hethrir's command of the Force was superior to theirs, however. He simply caused the twins' barrier to collapse as though it were made of sand.
Jacen Solo once protected both himself and Admiral Cha Niathal from an explosion in the hotel district south of the Galactic Senate, by wrapping their taxicab in a Force shield which absorbed the full brunt of the blast.
On the Xbox 360 and PS3 versions of Star Wars: The Force Unleashed both Jedi and Sith that Galen Marek fights utilize this technique. Rahm Kota, Shaak Ti, and even Darth Vader uses it, even using it to block off Galen's lightsaber and his Force Lightning The Emperor used a lightning variant of this power that also harmed the approaching opponent, aside from shielding the Dark Lord. It was often used by them when these masters were preparing for a powerful force attack; namely when Kota flings his 'saber in the air to initiate a ground slam, Shaak Ti, whenever she is preparing to launch a force sphere, Darth Vader, whenever he is about to unleash a blast of the Force, and the Emperor, whenever he is about to use Lightning Grenade.