What is the origination of the term "Commonwealth" such as in Virginia?

At the time democracy was a vision in the minds of 17th Century political theorists like John Locke, they were sensitive to the differences between a state controlled by a king and and one that derived it's power from the people. They used the term commonwealth to make that destinction. Four of our states chose to retain that description rather than "state."

Functionaly, there is no difference.