The term historical information refers to any information containing resources that may be utilized by a project team and or a project team leader for the purposes of garnering as much information as is possible about projects, activities, or events that had taken place in previous time periods for the purposes of providing adequate insight and background to the team when making decisions that will ultimately affect the course of the current project. The resources which may be utilized for the purposes o gathering this quantity of information can range from formal materials such as formal reports (this can include final reports that have been written and distributed externally, or more informal reports that have been written and disseminated internally), as well as other miscellaneous data, any assorted project files, historical records and notes, any written correspondence that may have been conducted (both written and electronic), and any previously closed contracts that may exist.
This term is defined in the 3rd and the 4th edition of the PMBOK.