Holocrons are rare artifacts created by the Jedi to store information, usually as holorecordings, though other forms are not unheard of. These artifacts are known for their exceptional durability and longevity, the secrets of which are known only to Jedi archivists; as such, holocrons are capable of retaining their data through tens of thousands of years, and are able to survive planet-wide catastrophes.
The great library in the Jedi Temple is home to dozens of these artifacts, each pertaining to a different facet of the Force. Access to these holocrons is restricted, but not impossible to gain if one has the temerity and good reason to beg permission of the Council. Exactly what subjects these holocrons teach is known only to the Council and the Archivists tasked with their protection, but it is rumored that not everything contained within is purely of the Light Side of the Force.