From BiblePortal Wikipedia
Webster's Dictionary 
(1): ( a.) Keeness and severity of remark; caustic exposure to reprobation; trenchant wit; sarcasm.
(2): ( a.) A composition, generally poetical, holding up vice or folly to reprobation; a keen or severe exposure of what in public or private morals deserves rebuke; an invective poem; as, the Satires of Juvenal.
The Nuttall Encyclopedia 
A species of poetry or prose writing in which the vice or folly of the times is held up to ridicule, a species in which Horace and Juvenal excelled among the Romans, and Dryden, Pope, and Swift among us.