The software and hardware of the OpenEnergyMonitor project are open-source.
Open-source software has been around for some time. The concept is simple to understand and relatively easy to implement. The source code with documentation is made available to all; usually a through a free online download.
Open-source hardware is a relatively new idea. Basically it entails the sharing of the hardware design (schematics, CAD files, documentation etc) so that the hardware can be reproduced and/or modified by someone else. Until now there has been no formal definition. A community derived official definition of open-source hardware is just been released:http://www.adafruit.com/blog/2011/02/10/open-hardware-definition-1-0-released/
Logo ideas for open-source hardware. To be printed on PCB's etc.
Below is another (newly submitted) logo I found on the forum
. I really like this one. I think it combines the best features of the best two designs above. The only problem I can see is the circles being mistaken for pads and drilled out while drilling the PCB!