A preamble is an introductory and expressionary statement in a document that explains the document's purpose and underlying philosophy. When applied to the opening paragraphs of a statute, it may recite historical facts pertinent to the subject of the statute. It is distinct from the long title or enacting formula of a law.

Preamble to the Charter of the United Nations
The Preamble to the Constitution of India. It is the longest written constitution of any sovereign country in the world.[1]

In parliamentary procedure using Robert's Rules of Order, a preamble consists of "Whereas" clauses that are placed before the resolving clauses in a resolution (formal written motion).[2] However, preambles are not required to be placed in resolutions.[2] According to Robert's Rules of Order, including such background information may not be helpful in passing the resolution.[2]