The task team or party responsible for authoring a specific model element, recorded so everyone knows who to ask about it and who's accountable for its accuracy. On a coordinated, multi-discipline project, it's not always obvious who "owns" a given wall or duct in the federated model - the Model Element Author designation (often a code or abbreviation on the element itself) removes the ambiguity, tying every element back to the specific task team responsible for its geometry and data.