Open hardware can mean different things to different people:
This is different from Open Source Hardware (OSHW), which is defined as:
"Open source hardware is hardware whose design is made publicly available so that anyone can study, modify, distribute, make, and sell the design or hardware based on that design. The hardware’s source, the design from which it is made, is available in the preferred format for making modifications to it." - OSHWA
Hardware does not need to be OSHWA certified to be open hardware, this certification is 100% optional.