A compact disc player, or CD player, is a device that is able to play audio in a format that has been recorded onto a compact disc. Compact discs are a type of digital media that were developed by a joint venture between Philips and Sony, being released to the commercial market in 1982. The format was originally developed solely for storing and playing audio, but was quickly developed into being able to store data that could be read by a computer.
There have been a number of iterations that compact discs have gone through, varying between only writable once and being rewritable multiple times. There were experiments involving data compression that have allowed more than the standard 700 MB of data, but this was generally not adopted due to the invention of the digital video disc, or DVD.
The compact disc is a plastic disc that has a metal foil on one side that has digital information stored on it that can be read by a laser. The speed at which compact discs were able to dominate the market has largely been credited to Sony and Philips working together 
to create a standard that could be easily followed by any company. This was one of the first instances of rival companies collaborating, but a needed one, as there have been many competing products over the years that whilst good, ultimately failed commercially due to high licensing costs for companies wishing to use the proprietary media format.
CDs were primarily a direct competitor to the cassette, although their disadvantage was the much higher cost of the player. For decades, CDs were the most common media in the audio market and it wasn’t until the turn of the millennium that that began to change. The proliferation of the internet and personal computers led to the development of audio files that could be played on the PC. The files being shareable over the internet helped to decrease the popularity of CDs, although they remained in popular use due to their portability until the rise of the MP3 player. Although CDs may have lost large parts of market share to MP3 and other digital file formats, they still remain highly popular today, although shops dedicated to selling physical music have decreased in more recent years.