In Microsoft Excel you reference columns as letters by default - A1, B3, C5, etc. But you can also reference the columns by there number instead of letter. This is called a R1C1 style cell reference in Excel and it is undoubtedly more complicated. However, it does serve a purpose and is often needed for complex array formulas within macros in Excel.
Steps to change columns from letter to numbers - R1C1 style cell references in Excel 2007:
Before:
After:
Excel Options Menu: