Initialism of advanced audio coding.
"The new streaming service uses AAC to provide high-quality sound at lower file sizes than MP3."
In plain English: AAC stands for augmentative and alternative communication, which is any method used to help people who cannot speak normally express themselves through signs or devices.
"The AAC device helped her communicate more clearly during our meeting."
American Cement Corporation, stock exchange symbol.
"Investors traded shares of the American Cement Corporation under the ticker symbol AAC on the New York Stock Exchange."
Initialism of American Alumni Council., now known as Council for Advancement and Support of Education
"The university archives listed the original founding committee under the initials AAC, which stood for the American Alumni Council before it was renamed."