As a data warehousing/BI specialist I'd like to share my interperetation.

'Data' data (as in your company's data warehouse) is primarily internal data. By this I mean: data generated primarily by your source systems or associated business processes.

'Big' data is external data. It is tweets that express opinion about your brand. Weather patterns that might influence supply logistics. Demographics of markets you wish to penetrate.

I think there are a great number of slightly different interpretations out there but pragmatically speaking, what I have suggested here makes sense.