| Suspend mode is a mode in which your computer can go into to conserve power. Depending on the machine, it can be almost as thorough as a power down, or as simple as simply shutting off the monitor. Suspend mode has gotten more advanced over the years; computers can now suspend entirely to memory and shut down everything else, using only a few watts while in suspend mode.
My Windows box powers down the CPU, all local disks, the CPU fan, and the monitor. The power supply stays on and the DVD-ROM drive still has power. The motherboard supports suspend to RAM but the power supply can't put out enough stand by power to utilize it.
Suspend mode is useful because machines tend to come out of it very quickly. I've started using it lately instead of hibernate which uses up disk space and still needs a POST to get out of. | 
