Energy Shield / Energy Barrier (called Evil Barrier or Explosive Wave in Budokai Tenkaichi 3) is a technique used to create an energy shield around the user to protect the them. This is first seen when Future Gohan fights the androids the second time. It is also seen in one of Vegeta's flashbacks being used by his father, King Vegeta. Goku also uses it in Movie 3, The Tree of Might. Gohan uses it to stop him, Krillin, and Piccolo from being sucked into the Dead Zone although this was most likely a stronger version as it was able to stop them from being pulled in the slightest.
Broly (as a baby, no less) uses it to save himself and his father, Paragus from a dying Planet Vegeta. Broly's energy shield even allows him (and others if he chooses) to survive in the vacuum of space (or even within molten lava).
It is seen several times in Movie 10 (this movie contains the best examples of the use of technique in the anime), first when Gohan uses it to shield Goten, Videl, and Trunks from one Broly's Blaster Shells (energy blasts); later Broly again uses it to escape from a sea of lava, and lastly, he briefly attempts to use it to block Gohan, Goten, and Goku's Family Kamehameha, but fails and is rocketed towards the Sun and is defeated.
In Dragon Ball Z: Wrath of the Dragon, Vegeta emits an Energy Barrier from his hands in a fashion similar to Final Flash to protect civilians from Hirudagarn.
The evil Wizard Babidi has a Yellow energy shield called Wizard Barrier (which is produced by his crystal ball). Bojack has his own energy shield called Psycho Barrier. Tapion's flute creates a blue energy shield, known as Hero's Flute.
Note: It seems that anyone who can use ki can use the technique, however it may require some practice and its strength is probably determined by the user.
