Definition of Extrinsic Ambiguity
In a written contract, such is an uncertainty which does not arise by the terms of the instrument itself but is created by some collateral matter not appearing in the instrument. Pacific Indemnity Co. v. California Electric Works, 29 Cal. App.2d 260, 84 P.2d 313, 320.
That's the definition of Extrinsic Ambiguity in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.