Initially, in the world of the characters in the novel, the A stands for adultery. The meaning, however, changes as the plot progresses and some in the story regard the A as meaning angel. From the...
"Access Server", "Aortic stenosis", "Adult swim" and "ActionScript"
Information Technology. There may be other abbreviations.
In the Nathaniel Hawthorne novel The Scarlet Letter, the red letter "A" on Hester Prynne's clothing stands for adulteress.
The letter ypsilon (ύψιλον).