Television channel
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The term television channel generally refers to either a television station or its cable/satellite counterpart (both outlined below). Sometimes, it is confused with the term television network, which (when properly utilized) describes a group of geographically distributed television stations that share affiliation/ownership and some or all of their programming with one another.
The term may also refer to a physical or virtual location over which a television channel (in the above sense) is distributed. For example, in North America, "channel 2" refers to the broadcast frequency of 55.25MHz video/59.75Mc. audio, and may be shared by many different television stations or cable-distributed channels depending on one's location and service provider. This terminology may be muddled somewhat in other juridictions, for instance Europe, where terrestrial channels are commonly mapped from physical channels to common numerical positions (i.e. BBC One does not broadcast on any particular "channel 1" (example) but is nonetheless mapped to the "1" input on most British television sets). On digital platforms, such (location) channels are usually purely arbitrary.
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Television station
A television station is a type of broadcast station that broadcasts both audio and video to television receivers in a particular area. Traditionally, TV stations made their broadcasts by sending specially encoded radio signals over the air, called terrestrial television. Individual television stations are usually granted licenses by a government agency to use a particular section of the radio spectrum (a channel) through which they send their signals. Some stations use LPTV broadcast translators to retransmit to further areas.
Television stations are now in the process of converting from analogue (NTSC, PAL, or SÉCAM) to digital (ATSC, DVB, or ISDB). In some countries, this is being forced on consumers and stations, while in others it is entirely voluntary.
In countries such as the United States, television stations usually just have one transmitter (or, more recently, two transmitters if the station broadcasts a digital signal in addition to its standard analog signal); most of these stations should be independent or affiliated to a television network such as ABC, CBS, Fox, or NBC. In other countries such as the United Kingdom, television stations are generally associated with a nationwide television network, through which they get all of, or at least significant amounts of, their programming. In those countries, the signals broadcast in different areas have no call signs or other individual traits known to the general public (although a network might have regional variations, possibly broadcast from several different transmitters) and therefore there is no strong network/station split.
In the United States, each nationwide terrestrial broadcast network can have a few "O&Os" — stations that it owns and operates, usually in the larger broadcast markets, like New York or Los Angeles.
Non-broadcast television channels
Because some regions have had difficulty picking up over-the-air signals (particularly in mountainous areas), alternate means of distribution such as direct-to-home satellite and cable television have been introduced. Television channels specifically built to run on cable or satellite blur the line between TV station and TV network. That fact led some early cable channels to call themselves superstations.
Satellite and cable have created changes. Broadcast stations in an area can sign up to be carried on cable (called "must-carry" in the U.S.), but content providers like TLC can too. They are not licensed to run broadcast equipment like a station, and they do not regularly provide content to licensed broadcasters either. Furthermore, a distributor like TNT may begin producing its own programming, and shows presented exclusively on cable/satellite by one distributor may be syndicated to broadcast stations.
From the definitions above, use of the terms "network" or "station" in reference to nationwide cable/satellite channels is technically inaccurate. However, this is an arbitrary, inconsequential distinction, and varies from company to company. Indeed, in the U.S. there is even some geographical separation among "national" cable/satellite channels, be it programming (i.e. the Fox Sports Net group of regional sports channels, which share several programs), or simply regionalized advertising inserted by the local cable company.
Should a legal distinction be necessary between a (location) channel and a television channel in this sense, the terms "programming service" (e.g. [1]) or "programming undertaking" (e.g. [2]) may be used instead.
A person viewing by cable or satellite might not know what kind of organization is responsible for a given program, especially if it is syndicated, so what seems to be a station or a network may be neither.