Command Line GPIO Access - Pin Types (Orange Pi)
The Allwinner SoCs divide their I/O pins into banks, somewhat like many smaller MCUs do.   In some Linux versions these designations are passed through in some cases, in others or at least other contexts they are simply re-numbered, probably starting with 0 for PA0, adding 32 for PB0, etc in order to yield a more usual /sys/class/gpio/gpio0 etc

Ultimately you'll have to consult the references (or source) of your particular operating system flavor, its device tree (if utilized, or legacy configuration if not) your board documentation, and possibly the relevant SoC datasheet.

One resource you probably want to consult is http://linux-sunxi.org/GPIO