It absolutely is there are hearsay rules both federally and at the state level that determine what weight to give hearsay. Criminal law is different, but even then hearsay can be admissable, it just isn't by default.

Federal rules of evidence basically 801 to 807, 803, 805 and 807 (?) are specific exemptions. Notably in civil court they'd object to hearsay and the resolution is to call the person who is claimed to have said or done whatever as a witness and get their testimony making it no longer hearsay.