Hearsay
An out-of-court statement offered to prove the truth of the matter asserted; generally inadmissible.
The hearsay rule guards against unreliable evidence not tested by cross-examination. Key carve-outs include non-hearsay by definition (prior inconsistent statements under oath, party admissions) and the many exceptions (present sense impression, excited utterance, statements for medical diagnosis, business and public records, dying declarations). The Confrontation Clause adds a constitutional bar to testimonial hearsay against a criminal defendant absent confrontation.