Bond Ladder

What Does Bond Ladder Mean?
A strategy for managing fixed-income investments by which the investor builds a ladder by dividing his or her investment dollars evenly among bonds or CDs that mature at regular intervals simultaneously (for example, every six months, once a year or every two years).

Investopedia explains Bond Ladder
Advantages of bond ladders are consistent returns, low risk and ongoing liquidity because every interval you have securities expiring. The bond ladder also protects the investor's bond portfolio from call risk: since maturies are staggered, there is little chance that all bonds in one portfolio will be called at once.