Database provides a systematic and organized way of storing, managing and retrieving from collection of logically related information.
Secondly the information has to be persistent, that means even after the application is closed the information should be persisted.
Finally it should provide an independent way of accessing data and should not be dependent on the application to access the information.
Main difference between a simple file and database that database has independent way (SQL) of accessing information while simple files do not File meets the storing, managing and retrieving part of a database but not the independent way of accessing data. Many experienced programmers think that the main difference is that file can not provide multi-user capabilities which a DBMS provides. But if we look at some old COBOL and C programs where file where the only means of storing data, we can see functionalities like locking, multi-user etc provided very efficiently. So it’s a matter of debate if some interviewers think this as a main difference between files and database accept it… going in to debate is probably loosing a job.