1) Airlines and stock exchanges generate large amounts of data, with airlines collecting 10 terabytes per 30 minutes of flight time and the NYSE generating 1 terabyte of trade data daily. 2) Big data refers to a firm's ability to store, process, and access large amounts of data to make effective decisions and serve customers. What constitutes "big data" can be measured in bytes, kilobytes, megabytes, terabytes and larger units. 3) Hadoop is an open-source software framework for distributed storage and processing of large datasets across clusters of computer servers using simple programming models. It allows for the distributed processing of large datasets in a reliable, fault-tolerant manner.