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Incomputer science, astream is asequence of potentially unlimiteddata elements made available over time. A stream can be thought of as items on aconveyor belt being processed one at a time rather than in large batches. Streams are processed differently frombatch data.

Normal functions cannot operate on streams as a whole because they have potentially unlimited data. Formally, streams arecodata (potentially unlimited), not data (which is finite).

Functions that operate on a stream producing another stream are known asfilters and can be connected inpipelines in a manner analogous tofunction composition. Filters may operate on one item of a stream at a time or may base an item of output on multiple items of input such as amoving average.

The term "stream" is used in a number of similar ways:

• "Stream editing", as withsed,awk, andperl. Stream editing processes a file or files, in-place, without having to load the file(s) into a user interface. One example of such use is to do a search and replace on all the files in a directory, from the command line.
• OnUnix and related systems based on theC language, a stream is a source orsink of data, usually individual bytes orcharacters. Streams are an abstraction used when reading or writing files, or communicating overnetwork sockets. Thestandard streams are three streams made available to all programs.
• I/O devices can be interpreted as streams, as they produce or consume potentially unlimited data over time.
• Inobject-oriented programming, input streams are generally implemented asiterators.
• In theScheme language and some others, a stream is alazily evaluated ordelayed sequence of data elements. A stream can be used similarly to a list, but later elements are only calculated when needed. Streams can therefore represent infinitesequences andseries.^[1]
• In theSmalltalkstandard library and in otherprogramming languages as well, a stream is anexternal iterator. As in Scheme, streams can represent finite or infinite sequences.
• Stream processing — inparallel processing, especially in graphic processing, the term stream is applied tohardware as well assoftware. There it defines the quasi-continuous flow of data that is processed in adataflow programming language as soon as theprogram state meets the starting condition of the stream.

This sectionneeds expansion. You can help byadding to it.(February 2014)

Streams can be used as the underlying data type forchannels ininterprocess communication.

The term "stream" is also applied tofile systemforks, where multiple sets of data are associated with a single filename. Most often, there is one main stream that makes up the normal file data, while additional streams containmetadata. Here "stream" is used to indicate "variable size data", as opposed to fixed size metadata such asextended attributes, but differs from "stream" as used otherwise, meaning "data available over time, potentially infinite".

• Bitstream
• Codata
• Data stream
• Data stream mining
• Traffic flow (computer networking)
• Network socket
• Streaming algorithm
• Streaming media
• Stream processing

• An Approximate L1-Difference Algorithm for Massive Data Streams, 1995 Feigenbaum et al.

• Computer data
• Inter-process communication

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