Secondhand information that a witness only heard about from someone else and did not see or hear himself. Hearsay is not admitted in court because it's not trustworthy, as well as because of various constitutional principles such as the right to confront one's accusers, however, there are so many exceptions that often times hearsay is admitted more than excluded.
A statement, other than one made by the declarant while testifying at the trial or hearing, offered in evidence to prove the truth of the matter asserted. - 28 USC
Hearsay is any statement made outside a hearing or trial which is presented at the hearing or trial to prove the truth of the contents of the statement. All evidence rules begin with the premise that hearsay cannot be used in court because secondhand testimony is considered unreliable and because the person who made the original statement is often unavailable for cross-examination. Statements in the forms of letters, affidavits, declarations, diaries, memos, oral statements, notes, computer files, legal documents, purchase receipts and contracts all constitute hearsay when they are offered to prove that their contents are true.
Testimony during a hearing or trial is not hearsay unless the witness tries to repeat something someone else said or wrote. In addition, a statement introduced to prove something other than its truth is not hearsay. For example, testimony may be offered to show the speaker's state of mind.
Example: Dana and Bruce were fighting, and Dana shouted "Bruce, you are a lousy bastard." Marla heard the argument and was asked to testify at Dana and Bruce's divorce trial. Marla was permitted to repeat the statement "Bruce, you are a lousy bastard," because it is not hearsay. It was not introduced at the trial to prove that Bruce has lice or is an illegitimate child, but rather to show that Dana was angry.
A witness's earlier out-of-court statement may be presented at a trial or hearing if it contradicts his in-court testimony because the statement is being used to cast doubt on the witness's credibility rather than prove the statement's truth or falsity.
A great many exceptions to the hearsay rule exist and much hearsay tends to be admitted under these exceptions. Evidence which qualifies as exceptions is usually statements which are reliable and believed to be unfabricated. Some common exceptions are: