AVPU

Just one way of monitoring how responsive a casualty is.
A - Alert
V - Voice
P - Pain
U - unresponsive/unconscious.

Ok, so it seems like double-dutch, but really it's quite simple.
1)If your casualty is alert, they will be fully responsive to anything you do, e.g. they will be able to answer any questions you ask them, and hit you back if you try a pain response.

2)If your casualty is not fully alert, but there is a sign of life when you speak to them, then your casualty is responsive to voice, e.g. if you ask them to open their eyes, they might be able to flutter their eyelashes or something.

3)If your casualty is not fully alert, or doesn't respond to voice, then you get to beat them up. Ok, not like a punch bag, but you can pinch sensitive points on the body, such as the bottom of a fingernail, or the ear lobe, or you can rub their sternum (chest bone), all of which are particularly painful. If your casualty pulls away slightly, or makes a noise, or pulls a face, then they are responsive to pain.

4) Finally, if you've spoken to them, pinched them, generally tried to arouse them, and your casualty still hasn't responded, then they're out cold and unconscious. And that's when you worry.