The concept of information is still lacking a complete understanding, as witnessed by the large number of different meanings that overload the terms "data", "knowledge", and "information". In this paper, a definition of information (named epistemic information) based on the knowledge states of agents is proposed. It is used to analyze, understand, and explain some puzzling phenomena, like the subjectivity of information, and the inconsistency between amount of information contained in a datum and amount of information received. A "knowledge conservation principle" is also proposed and justified.