What is the difference between *.sqlite and *.db file?

A .sqlite file is as the name implies a file that contains an SQLite database.

The .db file extension is used by Oracle, Paradox and XoftSpySE databases.[1]

As Christian noted usually extensions aren't that important in the grand scheme of things and programs can open files with different extensions. So if you are thinking about changing extensions from .sqlite to .db it's probably fine as long as you follow the pattern Christian noted.

You can name your SQLite database whatever you want. The content is not determined by the file ending but by a sequence of bytes which start every SQLite (3) file:

0x53 0x51 0x4c 0x69 0x74 0x65 0x20 0x66 0x6f 0x72 0x6d 0x61 0x74 0x20 0x33 0x00

which is ASCII for:

• SQLite format 3

In other words, it could be the same database content. There is no difference, as long as the creator did not put other bytes in it.

If you want to see if it is a SQLite 3 database, open the file in a hexeditor and look for the byte above or simply open it with the SQLite driver.