Zero-latency SQLite storage in every Durable Object

What is the difference between a "durable object" and a file?

You can read the full article for an answer to that: https://blog.cloudflare.com/sqlite-in-durable-objects/

Short version: it's replicated to five data centers on every transaction, and backed up as a stream to object storage as well.

So it's a file that gets backed up like dropbox

At a very high level, yes. But the details matter here - you commit a transaction to the SQLite database and know that the commit has been pushed out to 3/5 replicas by the time the write API request returns - and that it will be logged to object storage (supporting 30 days of rollback) within ten seconds. AND it will live in a data center physically close to the user who caused it to be created.