What does "Output has been suspended by pressing Ctrl+S" mean?

I have encountered this for the first time in Ubuntu 13.10.

What is the meaning of this message across the top of the terminal? Is it a warning or a suggestion?

Unless I press Ctrl+Q, it doesn't give me a prompt to enter.

Solution 1:

In a standard "shell" the CTRL+S and CTRL+Q sequences are used to pause output to the screen. By pressing CTRL+S the output is paused, and CTRL+Q re-enables output.

It was very useful in the days of standard ASCII terminals / green screens which didn't have a nice scroll bar on the edge of the window :)

Solution 2:

It's a common feature to stop unwanted output (in some cases it might be very useful). You can often have the same effect with the Pause/Interr command on the keyboard.
Press CTRL+Q to resume the normal output/input and don't worry, it's normal. Good working...

Solution 3:

When one processes Ctrl+S, it suspends the screen from drawing. In this case, the screen will appear to be frozen.

This warning message is there just in case you did this by accident. This happens more often than you might think and it's can be very inconvenient because without knowing what happened you'll simply think that the terminal window has frozen and decide to close it.