[dmd]

Er - you know a magnetron doesn’t actually spin, right?

[estimator7292]

Ackshully that's not strictly true. Some (very) old models did not rotate the food, but instead rotated the microwave emitter in the top of the cavity.

[WorldMaker]

As a first approximation of referring to magnetic fields and their flux and inertia, "spins" is still a useful and common word for that. But yes, not necessarily the best technically correct word.