Open source hardware is a term we've used here on MAKE & CRAFT for describing some of the projects featured as well as some of our electronics kits and it was the subject of a talk we participated in at then SXSW conference, but what is it?
There are a few definitions, some come from "open source software" which is usually considered software's - "source code under a license (or arrangement such as the public domain) that permits users to study, change, and improve the software, and to redistribute it in modified or unmodified form"