Streaming is the process of delivering digital multimedia content from a provider to a consumer over a network. The provider may have the data stored or may be relaying it from a live source.
In computer science, streaming is the process of sending or receiving a sequence (stream) of data elements made available over time. A stream can be thought of as a conveyor belt that allows items to be processed one at a time rather than in large batches which must be completed in whole before subsequent data transfer occurs.
Streams are processed differently from batch data – normal functions cannot operate on streams as a whole, as they have potentially unlimited data, streams are codata (potentially unlimited), not data (which is finite).
More details in Wikipedia page on streaming media