A written or printed statement made under oath.
A written declaration made under oath before a notary public or other authorized officer.
Duhaime Legal Dictionary
The statement is intended to become evidence before a Court.
It is also certified by a notary or lawyer or some other judicial officer that can administer oaths, to the effect that the person signing the affidavit was under oath when doing so (as is shown on the bottom of the sample affidavit form pictured left).
These documents carry great weight in Courts to the extent that judges have been known to (albeit rarely) accept an affidavit instead of the testimony of the witness.
Medieval Latin, he/she has pledged faith, third singular perfect of affidare see affiant
: a sworn statement in writing made esp. under oath or on affirmation before an authorized magistrate or officer (compare deposition examination)
n. 1) any written document in which the signer swears under oath before a notary public or someone authorized to take oaths (like a County Clerk), that the statements in the document are true. 2) in many states a declaration under penalty of perjury, which does not require the oath-taking before a notary, is the equivalent of an affidavit.
A sworn statement in writing made especially under oath or on affirmation before an authorized magistrate or officer
The Free (Legal) Dictionary
An affidavit is voluntarily made without any cross-examination of the affiant and, therefore, is not the same as a deposition, a record of an examination of a witness or a party made either voluntarily or pursuant to a subpoena, as if the party were testifying in court under cross-examination. A pleading—a request to a court to exercise its judicial power in favor of a party that contains allegations or conclusions of facts that are not necessarily verified—differs from an affidavit, which states facts under oath.
In American jurisprudence, under the rules for hearsay, admission of an unsupported affidavit as evidence is unusual (especially if the affiant is not available for cross-examination) with regard to material facts which may be dispositive of the matter at bar. Affidavits from persons who are dead or otherwise incapacitated, or who cannot be located or made to appear may be accepted by the court, but usually only in the presence of corroborating evidence. An affidavit which reflected a better grasp of the facts close in time to the actual events may be used to refresh a witness' recollection. Materials used to refresh recollection are admissible as evidence. If the affiant is a party in the case, the affiant's opponent may be successful in having the affidavit admitted as evidence, as statements by a party-opponent are not considered hearsay.