Which term refers to the sum of all money held by businesses and individuals, including traveler's checks and checkable deposits?

The correct term for the sum of all money held by businesses and individuals, including traveler's checks and checkable deposits, is M1. M1 is the most liquid measure of money supply and comprises physical currency, demand deposits, and various other forms of money that can quickly be spent. This definition underscores its role in facilitating transactions, highlighting why it is a crucial component in understanding the economy.

The other measures of money supply, such as M2, M3, and M4, include broader definitions that encompass other types of accounts and savings, which are less liquid. M2, for example, includes savings accounts and time deposits alongside M1, significantly expanding the scope of what is counted as money but not directly tied to the most liquid forms in immediate circulation.