What does it mean if you get a blue screen on an iPod touch 4th gen?

It means that your iPod has crashed and you may lose data. This happens when an app malfunctions, the system's board crashed, or some other problem that may have affected the interface. It's a software problem and recent updates have addressed it and future ones will do the same.

To fix this problem, your best bet is to restart your device. Obviously in a blue screen mode, you can't really see anything but that doesn't mean that under the blue screen there isn't the actual display. Hold the power button for a few seconds and it would be safe to assume the slide to shutdown would appear (but not visible on the blue screen). Just slide across the top like your normally shutting it off.

If that doesn't work, you may need to restore your iPod through iTunes. Normally, iTunes makes it mandatory to have a backup whenever you sync so it should work out fine. Plug in your iPd to your computer and go to iTunes. On the left you should see your iPod enlisted. Click it and the main page should come with all the iPod's general data. Somewhere visible, you should see a restore button. Apple has made it simple from there and restoring shouldn't take far too long.

If that doesn't work, you're out of luck. Your best bet then would be to go to an Apple Retail store and tell them the problem. They should be able to fix it, but you may lose a lot of your data (apps, contacts, photos, etc.).

Good luck.