[Lat. documenta, from docere, to show.] Written instruments adduced for the purpose of allowing or proving a claim or title, or other matter in controversy; evidences of title. This term was anciently applied in particular to the evidences of title to real property, or muniments of title, (quibus jus prodiorum firmatur,) and otherwise called telligrapha. Documents are a species of instruments of evidence, and, according to a modern writer on evidence, properly include all material substances on which the thoughts of men are represented by any species of conventional mark or symbol. Thus, the wooden score on which a baker and his customers indicate by notches the number of loaves of bread supplied, the old exchequer tallies, and such like, are documents as much as the most elaborate deed.

Law Dictionary, Of principal terms of common law and maxims, part 1, J.S. Voorhies, NY, 1850

A legal document is the written, physical embodiment of information conforming to the principles of law enacted by the government through the legislative process and reviewed by the judicial system. The legal document stands at the juncture between the rule of law and its practical application in our daily lives. It is the legal document, as an instrument or a pleading, that brings the black letter of the law into physical existence to accomplish a stated result consistent with that law. In the written document, the law finds its most meaningful expression.

Basics of Legal Document Preparation, By Robert R. Cummins, 1997

Determining the true meaning of a legal document is an issue of law, not fact, and the EUC is a legal document, albeit a fairly short and simple one. But it is only in a limited sense the true meaning of a single ordinary word (or here pair of words, “residential houseboats”) in a legal document is a question of law.