NAK /nak/ interj. [from the ASCII mnemonic for 0010101] 1. On-line joke answer to {ACK}?: "I'm not here." 2. On-line answer to a request for chat: "I'm not available." 3. Used to politely interrupt someone to tell them you don't understand their point or that they have suddenly stopped making sense. See {ACK}, sense 3. "And then, after we recode the project in COBOL...." "Nak, Nak, Nak! I thought I heard you say COBOL!"