Definition of Hearsay
Hearsay is a statement made by a witness who does not have first-hand knowledge of the incident in question. Hearsay is usually not admissible as evidence in court under the hearsay rule. An example of hearsay could include testimony from a witness that someone told them another person was driving the car at the time of an accident. But because they did not see the persona actually driving the car this testimony is considered hearsay evidence and is not admissible. Now if the witness actually saw Tom driving the car this evidence could be admitted as evidence because it was eye witness testimony.
Some types of hearsay are admissible. For example a birth certificate or a marriage license are technically second hand pieces of information, but they are considered legal documents and it would be difficult to find actual attendees of either event. The United States has lists of exceptions to the hearsay rule.