Increased use of technology by individuals, companies, and other organizations, together with the proliferation of smart devices and Internet access has led to a massive growth in the volume of data that can be generated, captured, and analyzed. Much of this data can be processed in real-time (or at least, near real-time) as a perpetual stream of data, enabling the creation of systems that reveal instant insights and trends, or take immediate responsive action to events as they occur. Which definition of stream processing is correct?