What is heresay in a court of law?

'Hearsay' is secondhand information that a witness only heard about from someone else but did not see or hear themselves. Hearsay is not admissabile in court because it's not trustworthy, as well as because of constitutional rights such as the right to confront one's accusers, however, there are so many exceptions to this general rule that oftentimes hearsay can be admitted. See: http://www.lectlaw.com/def/h007.htm