The Annual Percentage Rate (APR) is a measure used to express the cost of borrowing money or the return on an investment over a year. It includes not just the interest rate but also any additional fees or costs associated with the loan or investment, making it a more comprehensive figure for comparison. APR is commonly used in various financial products, such as credit cards, mortgages, and personal loans. By providing a standardized way to compare different offers, APR helps consumers make informed decisions about which financial products best suit their needs.