pre·am·ble   (prē'ām'bəl, prē-ām'-)    n.   A preliminary statement, especially the introduction to a formal document that serves to explain its purpose. An introductory occurrence or fact; a preliminary. [Middle English, from Old French preambule, from Medieval Latin praeambulum, from neuter of praeambulus, walking in front : prae-, pre- + ambulāre, to walk; see ambulate.] pre·am'bu·lar'y (-byə-lěr'ē) adj.

preamble 

Main Entry: pre·am·ble
Pronunciation: 'prE-"am-b&l, prE-'am-
Function: noun
Etymology: Middle French preambule, from Medieval Latin preambulum, from Late Latin, neuter of preambulus walking in front of, from Latin prae- + ambulare to walk
: an introductory statement (as to a contract); especially : the introductory part of a constitution or statute that usually states the reasons for and intent of the law
NOTE: While preambles do not state law and therefore are not judicially enforceable, they are used to determine legislative intent when interpreting statutes.