What’s VQ_VERYLOWDISK & why is it in my log?

For example:

9/4/10 1:48:31 PM KernelEventAgent[72] tid 00000000 received event(s) VQ_LOWDISK, VQ_VERYLOWDISK (516)

This indicates that Mac OS X has detected a drive (hard drive, RAM drive, Zip Drive, etc), that is very low or out of disk space.  If this is your boot drive, you will receive a POP up warning message that the disk is out of disk space.

How to fix this?  Free some disk space up from the drive in question, burn files to DVD, Delete unnecessary files or move them to a external drive.