Defendant

The person who is sued in a civil action or charged with a criminal offence.

The person being sued by the plaintiff in a civil lawsuit. In the style of cause Smith v. Jones, one can assume that Jones is the defendant being sued by Smith (but this is not necessarily always the case since Smith could have originally been a defendant, and if Smith lost at trial and there was an appeal decision, the appellant in some jurisdictions is sometimes the first named party in the style of cause).