ok, didn't know that, though would he still have had a vest date then?

ex. lets say meta vests one per month on the 15th, and he starts on the 14th, would he normally have vested right away, or would he have had to wait to Dec 15th? (and can apply to whatever schedule you want, just picked a monthly one for example sake).

I don't know how you've seen it, but I've seen it mean exactly that. A one-year cliff means that your whole year (usually your first) vests at once, in one day.

No, that’s not what a cliff is. https://www.investopedia.com/terms/c/cliffvesting.asp

What you’re talking about is front-loading or ballooning vesting schedules.