FM Synthesis

Frequency modulation synthesis (aka FM Synthesis, OPL-Synth) is a form of audio synthesis where the timbre of a simple waveform (such as a square, triangle, or sawtooth) is changed by modulating its frequency with a modulator frequency that is also in the audio range. In simple words, it's a generation of audio stream from scratch by formulas (while Wave-Table based synthesis is based on pre-recorded samples (aka Sound Fonts)).

Links

 * More detail description about FM Synthesis at Wikipedia
 * Yamaha YMF262 (OPL3) - most popular FM Chip on PC Audio cards like Sound Blaster
 * Yamaha YM2612 (OPN2) - a chip used in the Sega Genesis game console