Not sure exactly what is meant, but if this includes Certificates of Deposit, CD laddering was a frequent thing when interest rates were high enough to be worthwhile, where you'd want long-term CDs for the highest interest rates, but wan t to get the point of having some fraction of your CDs expire every month so you have liquidity, so you might have 60 5-yr CDs for instance, and somewhat less while you're working your way up to that
