Define the term preamble

a preliminary or preparatory statement; an introduction.

or;

The preamble is not actually a law or a legal document, but it is used to make it clear what to expect in the Constitution. Namely, the preamble says that the Constitution aims to create laws around justice, peace, defense, welfare, liberty, and prosperity for a "more perfect" country for Americans.

The preamble is an introduction to a document that describes the documents purpose.