What does "DOE compliant" mean in Disk Utility?
DOE is a method to wipe disks, developed by Department of Energy as part in their manual to ensure the confidentiality of Department of Energy information.

From macs.about.com :


  When Disk Utility uses the DOE-compliant 3-pass secure erase, it will write two passes of random data and then a single pass of a known data pattern. This will take anywhere from a day to a week or more, depending on the size of the drive. You can run this stress test in the background while you use your Mac for other activities.