The term originally came about in the early days of top 40radio formats when stations would devise (and, eventually, publish) a limited list of songs to be played. The term would go on to refer to the entire catalog of songs that a given radio station (of any format) would draw from. Additionally, the term was used to refer to an ordered list of songs played during a given time period. Playlists are often adjusted based on time of day, known as dayparting.
As music storage and playback using personal computers became common, the term playlist was adopted by various media playersoftware programs intended to organize and control music on a PC. Such playlists may be defined, stored, and selected to run either in sequence or, if a random playlist function is selected, in a random order. Playlists' uses include allowing a particular desired musical atmosphere to be created and maintained without constant user interaction, or to allow a variety of different styles of music be played, again without maintenance.
Some websites allow categorization, editing, and listening of playlists online, such as Project Playlist, 8tracks, Plurn, imeem and Webjay. Other sites such as Musicmobs focus on playlist creation aided by personalized song recommendations, ratings and reviews. Another site, PlaylistHQ, creates playlists based on upcoming concerts. On certain sites, users create and share annotated playlists, giving visitors the option to read contextual information or reviewer comments about each song while listening. Some sites only allow the sharing of the playlist data with the actual music being delivered by other channels e.g. plurn, others provide a closed catalog of content from which the playlists can be generated while sites like imeem allow users to upload the music to central servers to be shared and accessed by any user of the site.
iPods can also be used to build playlists. The iPod software, "iWorkOut Muse", uses playlists to help people work out to music.
On video hosting service websites such as YouTube and Vimeo, users can make playlists of select videos from themselves or other users for topical purposes; paid accounts can upgrade playlists of their own videos to "shows".
The idea of generating automatically music playlists from annotated databases was pioneered by Pachet and Roy.Constraint satisfaction techniques were developed to create playlists that satisfy arbitrary "sequence constraints", such as continuity, diversity, similarity, etc. Since, many other techniques were proposed, such as case-based reasoning.