How many people have you asked what it meant? Because I'd be willing to bet the answers would be all over the place with respect to how many weeks are ok.

I for one won't take an offer that includes "unlimited" PTO because it's a lie, and it means I can't compare the offer to my current job, and an employer offering it has a good chance of being underhanded. If they're not, they should be willing to put a specific number in my contract.