This is the ability for parts of a synthesizer to be able to modulate other parts of the synthesizer. The synths with most cross-modulation abilities are modular synths, which actually use patch leads to plug different modules into each other, so any output can be plugged into any input....
Micromoog
This is Moog Music's "synthesizer for everyman. [The] design approach for the
Micromoog was to use a minimal number of functional building blocks and to configure
the instrument for the greatest amount of performer control over these blocks. The
Micromoog consists of the basic necessities: one voltage controlled oscillator (VCO),
one voltage controlled amplifier (VCA), two contour generators, and one sample and
hold. The 'open system' inputs and outputs make this Micromoog a basic musical
building block which can be expanded to meet the performer's growth."
This was the synth that followed the Minimoog. Having only one oscillator and using
less expensive materials, this became the cheap alternative to the Minimoog. It was
also one of the few and possibly the first of the early synths to use the pitch ribbon
controller instead of the more popular pitch wheel found on the Minimoog.