Hearsay
Hearsay in its most general and oldest meaning is an out of court statement used to establish the facts which that statement asserts.
Hearsay is generally not admissible as evidence in common law courts, but the rules for admissibility are more relaxed in court systems based on the civil law system.
The reason for the hearsay rule is that the credibility of the person or his observations cannot be challenged by the person against whom the testimony is being proffered.
While the 'hearsay rule' is commonly thought of within the context of "who said what to whom," in fact it is much more significant in its application to documents and electronic records. For example, many documents and entries on those documents are created by a machine or as part of a process where the person who actually created the document is unknown.
While hearsay is generally inadmissible as evidence in common law legal proceedings such as litigation there are many exceptions, some of which apply only when the original speaker (known as the depositions into the court record at trial.
Also a statement is not hearsay when it is not used to prove the statement that it asserts. For example, Y screaming that X shot B, cannot be used to establish that X shot B, but can be introduced to show that Y 'thought' X shot B. Similarly, a letters from a customer complaining that an employee was rude may be introduced as evidence that customers were complaining about the employee; this is not hearsay. It is only hearsay if the letter is introduced as evidence that the employee was rude.
In some jurisdictions such as Canada the limited exceptions format to the rule have been replaced by a more general theory of exceptions to the hearsay rule that allows courts to decide when documents, testimony or other evidentiary proof can be used that might not otherwise be considered. [more can be written about this].
Today the hearsay rule has developed into a complex set of evidentiary rules of admissibility that are used to prevent various types of statements and documents from being entered into evidence in various types of court proceedings, though they may be allowed in other types of alternative dispute resolution. Generally speaking hearsay is a concept that developed in the common law legal tradition in the context of the adversarial system of decision making.
