Where I live you are legally allowed to take as many days as you want forward. But you are allowed to take all of them at once if you want to, so most companies force you (they are allowed to do that) to take your vacation within the year, since otherwise people bunch it up and then leave for half a year of paid leave.

There was a guy in the newspaper a while ago who never took vacation for decades and ended up taking all days before retirement to retire a few years earlier.