It will give you the parameter name if you know the index, and it will give you the index if you know the name.
It will also give you other information such as parameter type, value and description.
The example I linked to uses a range of index numbers to list all of the parameter names for those numbers.
1 = A (length)
2 = B (width)
3 = ZZYZX (height)
I believe the index number is just the order that they are in the parameter list.
So if you know the position of the parameter in the list, you can use its index number to get the parameter name (and value, description, etc.).
But if you are trying to do this by API then you will need to ask in the Developer section of Archicad Talk.
Versions 6.5 to 22
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision M6800 - i7 4700MQ @ 2.40GHz, 16GB RAM, AMD FirePro M6100 (2GB), Windows 7 64bit