Back in the dark ages, a "zero day exploit" was a piece of malware which would lay in wait, doing nothing, counting down the days, until it hit day zero, and then it would trigger and do naughty things. Some folks also referred to this as a time bomb, but that was a less `|33+ term for it. We used to see a lot of these available on sites such as asta... never mind.
Fast forward to the era of "cyber" being hugely popular, and the massive flood of people doing short Kali or "Ethical Hacking" courses and getting into IT security jobs, and I see various formal IT security publications describing a zero day exploit as "ANYTHING which is known and not yet patched". To me, there is absolutely nothing about that description which relates to the "zero" or the "day" or the "zero day". I suspect this new terminology is the result of that influx of people with no background in either computer science or hacking, latching on to a cool sounding term and misunderstanding it completely.
What is your take on this? Do you go with the ye olde terminology, or the currently accepted terminology in fancy publications? Do you believe the meaning changed, and if so, when and how and why?