ACK /ak/ interj. 1. [from the ASCII mnemonic for 0000110] Acknowledge. Used to register one's presence (compare mainstream
*Yo!*). An appropriate response to ping or ENQ.
2. [from the comic strip "Bloom County"] An exclamation of
surprised disgust, esp. in "Ack pffft!" Semi-humorous.
Generally this sense is not spelled in caps (ACK) and is
distinguished by a following exclamation point. 3. Used to
politely interrupt someone to tell them you understand their point
(see NAK). Thus, for example, you might cut off an overly
long explanation with "Ack. Ack. Ack. I get it now".
There is also a usage "ACK?" (from sense 1) meaning "Are you
there?", often used in email when earlier mail has produced no
reply, or during a lull in talk mode to see if the person has
gone away (the standard humorous response is of course NAK
(sense 2), i.e., "I'm not here").