From Wikipedia:

In computing, a database is an organized collection of data stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques.

Or to put it another way, it’s a bunch of data, probably stored on a computer or some other place.

With such a broad definition almost anything can be considered a database.

Today’s databases blur the lines between technologies such as javascript and spreadsheets.

If your starting a new CRUD project try taking a look at something like MongoDB to simplify your design. Upsert makes a world of difference.

Retrofitting MongoDB over something like PostgreSQL is also worth considering if you have minimal touch points and don’t have exotic column lookup requirements.