From the game of Eschaton in David Foster Wallace's Infinite Jest. SACPOP stands for `strike against civilian population', and refers to nuking (or, by extension, aerially bombarding in any way) a large population centre of little or no military strategic value. IRL, the firebombing of Dresden is a classic example of a (conventional) SACPOP, as is the razing of Gernika. SACPOP against a relatively evenly-matched opponent easily leads to escalation and MAD.

See also countervalue.