Portenta pinouts for ADC
The &quot;high density&quot; connectors expose every pin of the MCU. The pins around the edge of the board duplicate just the immediately useful ones.
Every pin that is on the edge of the board is also on the high density connectors somewhere.
Why have the pin on both connectors? Simple: if you want to use it in a breadboard or with jumper wires then you want the useful pins on the edge. If you want to use a plug-in board then you don't want to have to connect to both the high density connectors and the breadboard connectors, that would just be really awkward (since both have completely different height profiles). So everything is on the high density connectors for plug-in boards, and the useful ones are also on the breadboard headers.
A0 is the Arduino name for the pin. ADC is the function of the pin. The A of ADC stands for Analog. It's a pin that Converts Analog to Digital. It's an Analog to Digital Conversion pin - ADC.