I'll try to explain better than the others.

In many cases/applications the data is saved into a database. Just imagine it like a notebook.
Now, in most databases you can write onto any page. In blockchain every time you write you add a full page at the end of that notebook.

This fact makes feasible to keep copies of this database/notebook on many computers around the world - keep it decentralized -, since at sync (whenever the wallet is started or a new block was found) just the missing pages at the end have to be added to the "notebook" (on a certain computer).

And yes, a "block" in the "chain" is such a "page" in the "notebook".