What do letters on the bottom of lottery scratch tickets represent?

It represents the amount of money you won. Some people only scratch off the bottoms to reveal the letters and don't bother with the top portion.

For instance if you scratch off the letters and "b" "q" "z" is revealed that ticket isn't a winner, but if you scratch off "t" "w" "o" you just won $2. Or "t" "w" "y" is $20. "C" "L" "M" stands for claim that's when you win the top prizes.

So generally any letter that doesn't spell money isn't a winner.