Group Art Unit
May be abbreviated "AU," "GAU" or "Grp Art Unit" on Office correspondence - a working unit responsible for a cluster of related patent art. Staffed by one supervisory patent examiner (SPE) and a number of patent examiners who determine patentability on applications for a patent. Group Art Units are currently identified by a four digit number, i.e., 1642.
Source: U.S. Patent and Trademark Office.