Microwaves, also known as Super High Frequency (SHF) signals, have
wavelengths
approximately in the range of 30 cm (1 GHz) to 1 mm (300 GHz).


if all microwaves are SHF, then there isn't any microwave oven that I know of
that actually uses microwaves. So why call it a microwave oven?

SHF starts at 3 GHZ (300 MHZ), not at 1 GHZ (100 ghz).

I've read that most microwave ovens operate in or around the 2.4 GHZ band
(which is UHF, not SHF).