Refers to statements made by persons other than the person testifying.  The statement is a mere repetition of what the witness has heard others say out of court.  Generally, hearsay evidence is not admissible and is excluded from consideration by the trier of fact.   However, there are numerous exceptions.  One such exception is a statement made for the purpose of medical diagnosis or treatment, including description of medical history, past or present pain, sensations, etc.