PCM

It actually isn't that easy as not all PCM data is equal. There are several parameters that a decoder must know in order to play that sound back properly, including:

* sampling frequency (also called sample rate)
* number of channels
* order of channels
* number of bits per sample (also called bit depth)
* signed or unsigned
* Endianess if bits per sample > 8
* PCM format (e.g. a-law, µ-law, linear, etc.)

PCM used on CDs isn't the same as PCM used on Blu-rays, for example.

Not one of those parameters is really optional. Sure, you can specify all of them manually when decoding (or when using tools such as sox to convert from raw PCM data to one of the containerized variants), but the container's whole purpose is to relief us humans of the need to keep that extra information around somehow. That's what the WAV container does. As do other container formats, but WAV one of the simplest one to use (within certain limits), making it especially suitable for people new to programming or new to audio processing.