An index refers to the position within an ordered list.
In the picture above, the index number is 4 for E.
An index starts at 0 and counts up 1 for each new element in the list.
In Excel, however, the Index starts at 1.
You can think of the table you are using as a grid.
With one index for up and down, and left and right.
Kind of like coordinates in battle ship!
So to break it down, using the table below we have:
Row Index [Value B]
2
Column Index [Value C]
3