Flat databases are like spreadsheets – tables that organize data in rows and columns. These are useful for simple tasks like tracking student sign ups or exit tickets, but not as useful for complex apps.

CSV files, spreadsheets, XML files and others can be examples of Flat databases. They don’t offer, by themselves, any computational way to update those rows or columns.

Relational databases use different tables that have some relationship to each other. For example in a photo-sharing app, there would be a table for users, one for posts, one for comments, etc. These would be stand-alone tables, but would be aware of each other by linking data, like a user_id value with a table that contained just posts.

Non-relational databases, also known as NoSQL databases don’t rely on structured tables. They use different forms of storing and linking information, sometimes stored as JSON objects like in Firebase or Firestore, for example.