Coming from the universe of Battletech and MechWarrior, "Aff" is an abbreviation of "Affirmative," meaning "yes." Its opposite, naturally, is "Neg," short for negative.
When expecting an answer one way or another, the prefix "qui" may be added.
Gunter: "Enemy Kodiak at 2 o'clock. Should I open fire, quiaff?"
Von Helsing: "Aff. Take out his legs."
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