[ATM] "At the moment"

[ATOP] "At time of posting..."

[attention whore] {n. phr.} {informal} Label given to any person who […]

[ATTN] "Attention"

[aught] See: [FOR AUGHT] at [FOR ALL] (2), [FOR ALL ONE […]

[Aunt Tom] {n.}, {slang}, {originally from Black English} A successful professional […]

[AUP] "Acceptable Use Policy"

[avail] See: [TO NO AVAIL] or [OF NO AVAIL].

[average] See: [ON AN AVERAGE] or [ON THE AVERAGE], [LAW OF […]

[awe] See: [STAND IN AWE OF].