Channels are basically outputs or pins. The ESP32 has 16 hardware PWM channels (Although my understanding is that Espressif has only implemented 8). You could actually create software PWM but then you would need to do all the work yourself.
 
As an example, let’s say you are building a robot with 8 servo’s. Each servo would require a separate PWM channel to operate independently. You attach each channel to a GPIO pin and then you can set each servo’s position with ledcWrite calls.

Hi Robert.
Yes, Steve is right.
You can think of channels as the “thing” that produces the signal. Then, we choose one GPIO when we will get the signal from.
This means that if you use the same channel for several GPIOs, they will all output the same signal.
I hope this is clear.
Regards,
Sara