(5) Agency statements of specific applicability, including advisory or legal opinions directed to particular parties about circumstance-specific questions (e.g., case or investigatory letters responding to complaints, warning letters), notices regarding particular locations or facilities (e.g., guidance pertaining to the use, operation, or control of a Government facility or property), and correspondence with individual persons or entities (e.g., congressional correspondence), except documents ostensibly directed to a particular party but designed to guide the conduct of the broader regulated public;
29 CFR § 1473.2
For purposes of this subpart, the term guidance document means an agency statement of general applicability, intended to have future effect on the behavior of regulated parties, that sets forth a policy on a statutory, regulatory, or technical issue, or an interpretation of a statute or regulation and is not otherwise required by statute to satisfy the rulemaking procedures specified in 5 U.S.C. 553 or 5 U.S.C. 556.