A more thorough explanation:

Definition: AAU is an abbreviation for "Amendment to allege use." It is a proposed modification to a registered trademark or an application for trademark registration.

Examples:

• Amendment of registration: This is when an existing trademark registration is modified to make minor changes in the design of a mark to reflect how the mark is actually used. For example, if a company's logo has changed slightly over time, they may file an amendment of registration to update the trademark registration.
• Amendment to allege use: This is a supplement to a trademark applicant's intent-to-use application filed to inform the U.S. Patent and Trademark Office that a trademark is actually in use in interstate commerce. For example, if a company filed an intent-to-use application for a trademark but has since started using the trademark in commerce, they may file an amendment to allege use to update their application.
• Amendment to different register: This is an amendment to an application for registration on the Principal Register, requesting that the mark instead be placed on the supplemental register. For example, if a trademark application is initially filed for the Principal Register but is later found to not meet the requirements for that register, the applicant may file an amendment to request placement on the supplemental register instead.

These examples illustrate how AAU can be used in different situations related to trademark registration and modification.