Area of Denial
From Diablo Wiki
Area of Denial, or AoD, refers to AoE attacks that take up some space on the screen, forcing players to move or avoid them.
Spells like Firewall and Acid Cloud are good examples of these. Even if the damage isn't that high, the fact that some amount of screen space is occupied will cause players to move away, which changes the play dynamics in various ways.
This is more of a game mechanical term than an actual game term. The D3 Team has mentioned it as a tool to mix up gameplay, and it's not normally a term players would use themselves.