"Autopilot" is understood to mean "the plane flies itself" by the general public. Here's one human pilot who's ticked off by it:

http://www.askthepilot.com/questionanswers/automation-myths/

On a sailboat "autopilot" generally means "keep this heading" or "keep this point of sail." I'm pretty sure in aviation it means "take me to this way point and elevation" or a sequence of such maneuvers. A plane flies itself or a boat navigates itself only so long as nothing unexpected occurs. In either case, a pilot must be standing by, maintaining awareness, ready to assume control and handle anything that may come up. I'm not sure what people think this means in terms of driving a car but I think it's early enough that Tesla can help define what this means.

Autopilot systems in aviation have become so complex and diverse that there is no single catch-all sentence to describe them. I guess you could come close with the phrase "a system designed to keep and guide the state of the aircraft within and through certain set constrains".

Those constrains could be constant like a certain heading or a direction (not the same thing by the way), a series of vectors or a single vector (like a flight-path or an approach to a runway) or constraints that depend on dynamic variables like controlling the altitude and speed according to the weight of the aircraft or automatically avoiding traffic.

Of course the pilot must be standing by because a) autopilots do not keep track of everything (and aviation control interfaces are quite complex) and b) sensors can and do malfunction.

> "Autopilot" is understood to mean "the plane flies itself" by the general public.

Just because people mistakenly believe something doesn't make it right. The general public once thought the Earth was flat, and how did that turn out?

You're right, Tesla mistakenly believed they could cash in on calling their system Autopilot™ and somehow sidestep the connotations with the name and the damage pushing a broken implementation on consumers is causing.

The unfortunate truth is, if I gave my mom a car with the autopilot feature, she'd end up eventually trusting it and not care about the implementation details that make Tesla's system not an automated driving feature. That's scary and dangerous to market to consumers.

>Just because people mistakenly believe something doesn't make it right.

Tesla promotes it as autopilot. Words matter.

If Tesla itself selectively denies that the common understanding is the meaning they intend, then they appear to be trying to have it both ways: cashing in on the PR and cachet that the common meaning confers, while disclaiming the responsibility that goes along with owners actually believing it.

Unlike the shape of the Earth, there is no truth of the matter regarding what a word means except common usage. In certain cases a word might have a technical definition beyond the usual consensus but 'autopilot' isn't one of those words and communications to the public in, say, an advertisement have to use the common meaning of words.