.WAV (or WAVE) is an uncompressed sound format, developed (or bought?) by the Microsoft Corporation.
Microsoft Pulse Code Modulation format.
Resources:
The Canonical WAVE File Format (www.lightlink.com 
) by Timothy John Weber
A compressed .Wav format is Adaptive Differential Pulse Code Modulation (ADPCM, see www.bdti.com )
Other uncompressed Sound File Formats are: .AU (Sun Microsystems) and .AIFF (Apple)
Well, you all know what way a sound can be pictured in a frequency curve. Wav, au and aiff files also represent the curve in an exact way, but, as a computer only can make discrete calculations, not in a continuous way, but cut up in tiny steps. Both the time, and the height of the curve is cut up in tiny steps. Sample rate tells what way the time is cut up. Bitdepth tells what way the height is cut up.
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<b>.MIDI</b> is a format that is developed to make electronical instruments communicate. So not the sound itself is encoded, but the actions; what key is pressed, the duration of a tone, et cetera.
Midi Resources:
Midi Specifications (circa 1995-2008)
Extensible Music Format (XMF)
Standard Midi Files Specification
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A .wav file is similar to a .bmp or a jpeg; it is a <b>recording</b>.
A .midi file is similar to a vector picture. You create a vector picture by drawing lines. You create a midi by playing an electronical instrument.
A midi and a wav are not 'played' in the same way; a midi is generated in a synthesizer, a wav is decoded from digital to analog.
When a midi is converted to a wav file, the midi file is played and the music is recorded as a .wav file. Similar if you write code to draw some lines, and save it as a bmp, not the lines are recorded, but the resulting picture is recorded.
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Apart from these formats there are also compressed formats; <b>MP3</b> is the best known nowadays. This is an MPEG format (Moving Pictures Expert Group). They use several smart algorithms, in three layers to encode a sound so they are experts indeed.
<b>Streaming media </b> Audio Files are huge. Streams make use of a buffer, so you can listen to a file, without having loaded the complete file. These streams are developed for use on on the internet extensions. Streams are also compressed.
. RA, . RM ( = real audio/real media; developed by Real Networks)
.WMA, .ASF ( = windows media audio)
.MOV ( = Quick Time)
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<b>Open format</b> Many of these formats are or were encumbered by IP/TM/patent issues that restricted their use. Free equivalents include:
FLAC (Free Lossless Audio Codec)
Ogg Vorbis (compressed format equivalent to VBR MP3)
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Also see:
the FAQ on Digital Signal Processing (www.bdti.com ).
Wikipedia: "audio file format" (en.wikipedia.org ).
A good link to all File Formats may be www.wotsit.org
<i>Anonymous Donor, Thank You so much for that link! -- Karl Knechtel</i>
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See original on c2.com