What is the "presumption of validity" as it relates to patents?

All patents are presumed to be valid, and so the burden of overcoming that presumption rests with the accused infringer (See Apotex USA, Inc. v. Merck & Co., 254 F.3d 1031, 1036 (Fed. Cir. 2001)).  This presumption can only be overcome with "clear and convincing evidence" of invalidity (Intellectual Property Development Inc. v. UA-Columbia Cablevision of Westchester Inc., 336 F.3d 1308, 1319 (Fed. Cir. 2003)).  The "clear and convincing evidence" standard is something less than "beyond reasonable doubt" (the standard employed in criminal cases) but something more than a "preponderance of evidence" (the standard employed in most civil cases).