I'm not sure on all these details, so if I'm giving out bad gouge somebody please call me on it, but here we go. A Midshipman is enrolled either at the Naval Academy or at a civilian university in Naval ROTC. It's more complicated in ROTC since many prior enlisted folks (those in the STA-21 program and I don't know who else) are enrolled as Officer Candidates instead of Midshipmen. All people coming from the civilian ranks (an a few prior enlisted people) are called Midshipmen. I believe that at the Academy, everyone's a Mid.
Historically, Midshipmen have been Naval Officers in training, but back before these programs were conducted ashore, they acquired their name based on the berthing arrangements in the sailing ships of yore. Officers bunked aft, enlisted forward, and those between the grades were berthed amidships hence the term "Midshipman." The Naval Academy Mids are the only Midshipmen currently on active duty, those in ROTC are technically in a reserve status. Don't know if they call the OCS guys Officer Candidates or Midshipman. There's my $.02, so hopefully it's all right.
If God isn't a Penn State fan, than why is the sky blue and white?