What is -12 volt setting on a motherboard?

[Clevor]

I have an A7V and AsusProbe 2.12. Recently, it pops up with the -12 volt setting flashing. It is telling me the -12 volt setting is out of the 10% tolerance. I don't know if this is real or maybe I just have to reinstall Asus Probe. But I have been having mysterious problems with my printer and PS/2 mouse not working occasionally. Can this be all related? What is the -12 volt setting and why is it important?