ATWATER, Calif. — A self-driving car is not a self-driving car is not a self-driving car.

That is the message Waymo, the autonomous vehicle division of Alphabet, Google’s parent company, tried to send on Monday, when it invited a group of reporters to visit Castle, a facility in California’s Central Valley that it has been using as a training course for its self-driving vehicles.

Castle, which is built on a decommissioned Air Force base roughly 120 miles from San Francisco, resembles a miniature city, with many of the realistic elements a self-driving car might encounter on the road — like cul-de-sacs, traffic signals and a smattering of potholes. Waymo has been putting its test vehicles through their paces here since 2013, and conducting some 20,000 tests of different road situations. And on Monday, the company was offering rides in its latest prototype, a Chrysler Pacifica minivan outfitted with a cluster of sensors and cameras.

But first, John Krafcik, Waymo’s chief executive, wanted to give a vocabulary lesson.

“Let’s talk about self-driving,” he said. “There’s a lot of confusion about what the terminology means.” He rattled off a list of terms that have been used to describe vehicles with varying levels of self-driving ability: autonomous, driverless, semiautonomous, fully self-driving, partially autonomous, semi-driverless.

“It’s really a bit of a problem, isn’t it?” he said.

If Mr. Krafcik seems annoyed, it’s because the self-driving hype cycle is running at full volume these days, with companies from Uber to General Motors to Tesla noisily promoting their progress toward autonomous vehicles.