When you "Dim" a variable using VBA it creates a spot in memory for this variable. Some programmers like to use short, one letter variables like i or j. I'd suggest you stick to variables like "LastRow" or "LastCol" or "RowCtr" so you can look at the code and understand it better. For the programmers who use i and j and k as variables, they are not as good at teaching and explaining what they are doing.
I'd suggest you NOT use the single letter variable names and create variables that are meaningful to you and your code. You will find reading code you wrote months or years ago will make a lot more sense when you revisit it.
Example - what would you rather read?
See http://www.ozgrid.com/VBA/variables.htm for more info about naming variables.