General Quarters is the ship's alert status. It is, basically, like Star Trek's “red alert” except this is what actual ships call it.

General Quarters can be called by any crew member, however it is generally called by the duty shift leader. Meaning, the pilot-in-command of the ship for the current shift. Typically, a crew member would contact the bridge and make a recommendation for general quarters rather than sounding it themselves. However, in the case of an emergency so drastic that seconds count – usually something engineering related – general quarters can be sounded without requesting it from the bridge.

The alert status can be called for basically any reason, but common reasons would be:

• Military/police inspection
• Responding to a distress call
• Mechanical failure of something important
• Training
• Hostile situation (i.e. pirates)
• Passengers being disruptive / fighting
• Medical emergency

When called, throughout the ship a message will play in a calm female voice:

General quarters, general quarters.  This (is/is not) a drill.
All passengers will please return to their quarters in a calm and orderly fashion.
Obey crew instructions at all time.

The message will repeat a couple times. The message may have some additions, with different meanings. These meanings are designed to not alert passengers to potentially hazardous situations that could cause panic. For example:

General quarters, general quarters.  This (is/is not) a drill.
All passengers will please return to their quarters in a calm and orderly fashion.
Obey crew instructions at all time.
All essential crew to muster stations.

This message means that crew with combat training should report to the deck 2 armory to be issued weapons.