Holocron is an item in Jedi Knight series games, which grants a player Force powers. Usually one holocron allows to attain one specific Force power with a certain level.
3 force power, based on the holocron type. They only appear in Holocron FFA.
Holocrons in JK series
In Jedi Outcast video game most of the Holocrons represent small boxes with a symbol for each Force power available in the game, which include Force Speed, Force Jump, Force Pull and Force Push as standard (neutral) powers, and Force Heal, Force Persuade for the Light Side. The abilities those of a Dark Side users are also available in game, like Force Grip and Force Lightning. In addition to these the Multiplayer offers additional powers, not included in Single Player campaign: Force Seeing, Force Protect, Force Absorb, Force Drain and Dark Rage.
These were later reintroduced in the Single Player campaign of Jedi Academy, though instead of holocrons, gained through a variety of Jedi trials, Players are offered to choose the powers from a special menu before taking a mission. Holocrons still remain in Multiplayer game modes though.
The predecessors of the JO/JA games such as Dark Forces and Dark Forces II: Jedi Knight offer no holocrons to the Player, as the first game is about a Rebel agent Kyle Katarn long before he found his potential as a Jedi Knight, and the sequel allows the Players to acquire the powers through the points they receive after completing a mission.
A Jedi Holocron, referenced by one of the New Republic troopers in DF II: JK add-on Star Wars: Jedi Knight: Mysteries of the Sith as the "Jedi Artifact", was a relic stolen by the Kaerobani pirates, which attacked the Corellian corvette during one of the missions. The item was later reclaimed by Mara Jade from a base on Rathalay.
In Star Wars
Holocrons made their first appearance in Expanded Universe stories of the Dark Empire comic books in 1991-1992. Since then the popular Jedi (and Sith) artifact has appeared in multiple Star Wars stories, such as Knights of the Old Republic and The Force Unleashed, usually providing the owner with knowledge on the Force, history or material on acquiring certain skills. The latest holocrons to appear in Star Wars are the ones seen in The Clone Wars and the plot episode of the Rebels series.