Recently, I experienced a communication failure talking to somebody about a "hard drive" until I could actually show the person what I was talking about.
"Oh, a hard disk! I thought you were saying something else, like 'hard drive.'"
"Yes, I probably did say hard drive."
What difference is there between these two, if any?
The title of the Wikipedia article uses the less concise "Hard disk drive" which I've also used, and could be disambiugated in this question/answer as well.
Here is a Google Ngrams view of the two terms, showing that "hard disk" used to be more common but "hard drive" is increasing in popularity and the edge that "hard disk" has now is mostly attributable to the fact that it comes first in "hard disk drive."
Cross-link to related question: Etymology of the use of "Drive" to refer to a digital storage medium