Whats the difference between FMU and IO servo rails on the Pixhawk 6C and 6C mini

Sorry if this is a basic questions. I can see from the pinout diagram and the docs of the PixHawk 6C that the motor signals are wired up to the IO PWM outputs and servos to the FMU. But what’s the actual difference between the two?
And what does FMU stand for?

I’ve often wondered the same,
From reading, it was said that the practical difference is that io pwm outs can pass through the rc inputs as a backup without the relying on the fmu. Whereas the fmu pwm cannot.
So in theory a plane with control surface servos on io outs could be manually landed even with a failed fmu or sensors etc

Ok thanks thats interesting.