Imposing a shout quota is a sanction for cases of shout abuse. A shout quota limits the frequency of a user's shouts (including "it"-type shouts). The typical limit imposed is 2 shouts per 60 seconds.
To see whether you have a shout quota of any kind, type "shout" or "it" alone without any message. If you have no quota, the response will be that you are not on the quota list and may shout your message. If you have a quota, the response will be the time when you may next make a shout - either right now or in a given number of seconds.
See also: etiquette, it, shout, shout abuse