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; the person who is being quoted is not in the court to validate whether or not the quote is accurate. Also, the person who is being quoted cannot be cross-examined since they are not there.
However, there are some exceptions to the hearsay rule, 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.