The term 'Till Stack' refers to the process of counting money in a cash register. The first step is to count the ONES, which are coins and bills of one denomination, such as pennies, nickels, dimes, quarters, and one-dollar bills. The second step is to count the tens, which are coins and bills of ten denominations, such as ten-dollar bills, twenty-dollar bills, and fifty-dollar bills. Once the ONES and tens have been counted, the total amount of money in the till can be determined.