According to Investopedia:

Borrowing money at a low interest rate from a credit card then investing that money at a higher interest rate to try to make a profit. The lowest risk and most common type of credit card arbitrage entails taking advantage of a 0% introductory APR balance transfer offer to borrow thousands of dollars from a credit card for the duration of the introductory period, often 12 or 15 months. The borrower then places all of this money in a higher-interest but no-risk vehicle, like a savings account, money market account or certificate of deposit, where the interest rate might be 1% to 5%, depending on market conditions. As long as the borrower makes all the required minimum monthly payments on the credit card on time and repays the balance in full before the introductory period expires, he or she will turn a profit from credit card arbitrage.

Taking free money from a credit card company via 0% APR balance transfer offers to invest in money market account.

Past Performance

Year Balance Net Profit Net Return
2015 $219,497 $17,951 8.18%
2016 $352,711 $25,464 7.22%
2018 $202,970 $22,883 11.27%
2018 $200,200 $16,608 8.20%