W is for… Waveforms
Vintage sound chips typically use simplistic waveforms such as triangle, square, sine and sawtooth. Later, sample-based chiptunes made use of single-cycle waveforms of all manner of shapes, often drawn by hand.
What sets sound chips apart from proper synthesisers is that the oscillators often sound quite rough and digital, and the resulting sounds are often simplistic because there's a lack of modulation options - and indeed things that can be modulated. Richer sounds can be created by stacking sounds across channels, detuning them, etc, but when you've only got a handful of channels to start with, this isn't always practical.
W is also for... Wizball
The C64 version of which features some terrific 'chip rock' courtesy of Martin Galway.