noun

1. The action of stopping operations; a closing, of a computer, business, event, etc.

   “You need to enter your password at startup, but it's not required at shutdown.”

2. A statement, insult, etc. that prevents the opponent from replying further.

   “When he insulted me, my reply was such a shutdown that he left the room.”

3. An autistic response to stress, etc. where the individual becomes silent and motionless.