What is resume= used for in my grub boot settings?

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http://unix.stackexchange.com – I've always noticed the resume=/dev/foo entry in /boot/grub/menu.lst, and that it corresponds to the swap partition, but I've never questioned its use. title SUSE Linux Enterprise Server 11 SP2 - 3.0.13-0.27 (default) root (hd0,0) kernel /boot/vmlinuz-3.0.13-0.27-default root=/dev/sda1 insmod=qla4xxx resume=/dev/sda2 crashkernel=256M-:128M showopts initrd /boot/initrd-3.0.13-0.27-default I was rebooting a server this morning and saw a boot message stating Starting manual resume from disk. Sounds like some sort of hibernate. So what exactly is resume? I'm trying to Google it (HowTos)