I find it easier to think about it from a data "usage" angle, "if you can query anything you like while running the 'database' on a single machine and get your

I find it easier to think about it from a data "usage" angle, "if you can query anything you like while running the 'database' on a single machine and get your answer within 24hrs your data is not 'big'" I used to see 24hr OLAP cube runs and no one ever called that 'big data'. It's entirely a question of scale in my mind, because these days you can buy truly gigantic servers, and they are phenomenally powerful but if your data needs multiple servers dividing the load in order to perform queries in a timely manner then you start talking about big data, it's a question of scale.