A pin is a pin on the controller/cpu.
Also known as GPIO (General Purpose IO).
The names follow a platform specific convention.
For Arduino platform it looks like:
A8 = Analog port 8
D2 = Digital port 2
You can also use AVR8 notation, when the Arduino has a AVR8 cpu.
For AVR8 platform it looks like:
PD0 = Pin 0 on port D.
PB2 = Pin 2 on port B.