Having X number of days off for vacation per year is an explicit contract. Company culture can still be broken enough to not allow you to use those days, but in most cases the expectation is that the vacation days you've been given are yours to use to the fullest (making reasonable accommodation for scheduling, etc).
"Unlimited" vacation is an implicit contract. You can take off as many days as is considered acceptable by the company or team culture. This number is not something you can know before you start your job, and it is something that can change as workplace culture evolves.
The "unlimited" part is also a load of bosh. If the company culture isn't completely sick nobody is going to begrudge you using up your X vacation days per year. But if you take more vacation than average at a place with "unlimited" vacation you run the risk of looking bad and suffering attendant consequences. (I hate that "looking bad" is even a thing apart from actual effectiveness, but unfortunately it's something we still have to worry about...)
"Unlimited" vacation is an implicit contract. You can take off as many days as is considered acceptable by the company or team culture. This number is not something you can know before you start your job, and it is something that can change as workplace culture evolves.
The "unlimited" part is also a load of bosh. If the company culture isn't completely sick nobody is going to begrudge you using up your X vacation days per year. But if you take more vacation than average at a place with "unlimited" vacation you run the risk of looking bad and suffering attendant consequences. (I hate that "looking bad" is even a thing apart from actual effectiveness, but unfortunately it's something we still have to worry about...)