From lifewire:

 'Big data' is the new science of understanding and predicting human behavior by studying large volumes of unstructured data. Big data is also known as 'predictive analytics'.

Analyzing Twitter posts, Facebook feeds, eBay searches, GPS trackers, and ATM machines are some big data examples. Studying security videos, traffic data, weather patterns, flight arrivals, cell phone tower logs, and heart rate trackers are other forms. Big data is a messy new science that changes weekly, and only a few experts understand it all.