In Chapter 13 -- The General Theory of the Rate of Interest -- Keynes wrote:
It should be obvious that the rate of interest cannot be a return to saving or waiting as such. For if a man hoards his savings in cash, he earns no interest, though he saves just as much as before. On the contrary, the mere definition of the rate of interest tells us in so many words that the rate of interest is the reward for parting with liquidity for a specified period. For the rate of interest is, in itself, nothing more than the inverse proportion between a sum of money and what can be obtained for parting with control over the money in exchange for a debt1 for a stated period of time.
The footnote attached to the above is as follows:
1 Without disturbance to this definition, we can draw the line between "money" and "debts" at whatever point is most convenient for handling a particular problem. For example, we can treat as money and command over general purchasing power which the owner has not parted with for a period in excess of three months, and as debt what cannot be recovered for a longer period than this; or we can substitute for "three months" one month or three days or three hours or any other period; or we can exclude from money whatever is not legal tender on the spot. It is often convenient in practice to include in money time-deposits with banks and, occasionally, even such instruments as (e.g.) treasury bills. As a rule, I shall, as in my Treatise on Money, assume that money is co-extensive with bank deposits.
So there is a "line" that separates money from debt. But this line can move. This line is a time-measurement: three months, or three days, or three hours, or "legal tender on the spot." Or three years, or thirty years.
If we move the line out to a long time-frame (as it is presently) then we think of most debt as money. People say things like "money is debt." And the factor-cost of money is high, because most of the stuff we use for money has interest costs associated with it.
If we move the line back to a short time-frame (as it was at the end of the second World War) then we do not think of debt as money. And little of the stuff we use for money has interest costs associated with it, so the factor-cost of money is low.
A low factor-cost of money is of primary importance for economic well-being.