It’s a central server i believe.

Well, it’s dumb data, so we don’t speak of federation (which happens between services), but basically yes.

Anyone can download the data and the TL;DR for your right to using the data is:

You are free to copy, distribute, transmit and adapt our data, as long as you credit OpenStreetMap and its contributors.

As a result, there are also many servers which mirror the data, i.e. provide a separate copy you can download, which is effectively like federation.