What is the Difference between SQL and NoSQL Database?

In a short way explained?

SQL only can store pre definded data which matching the structure of the database.

NoSQL can store "Documents" like json without predefine the structure and so you are able to deal with more complicated structures where you dont always know how exactly the data looks like you want to store, also its easier to extend.

As example if your data has changed and now it has one more field than the the old data, you have to adjust the sql to accept those new field. In comparison to nosql you can just safe the new data even without a adjustment in the nosql db.

But important is that those "lazyness" costs database speed, so if youre not indexing the nosql well, it would be slow as fuck, as if you got plenty of data. instead of the sql would be still fast.