Definition - What does Hearsay mean?
Hearsay refers to an out-of-court statement that's made in court in order to attempt to prove or disprove the truth of the matter asserted. In simple terms, hearsay means that someone testifying attempts to give the court a statement that someone else (who is not present in court) said.
The court generally does not allow hearsay since it can't be proved. There are some exceptions to hearsay, though, such as a spontaneous utterance while someone is dying. Such a statement may very well be permitted by a judge.
Justipedia explains Hearsay
As evidence, hearsay is considered inadmissible because it cannot be substantiated. Generally, attorneys will object with the reason being that the statement made on the stand is hearsay. However, sometimes judges will also stop someone on the stand who attempts to give hearsay.