Laddering is an investment technique that requires investors to purchase multiple financial products with different maturity dates or "rungs".
A person may purchase a shorter term bond in the event that he needs the capital soon to fund his children's tuition while purchasing other longer term bonds that mature later as retirement spending with a more favorable rate, assuming the economy is experiencing a normal yield curve during this time.
The idea is to separate CDs, cash, bonds, annuities, and others into different "ladders" (or "buckets" or "baskets") depending on when the asset is expected to be liquidated to fund the retirement revenue stream.
Low-risk assets are used at the start of retirement (and usually have an expected lower rate of return, due to lacking a risk premium).
Generally an initial investment of $10,000-$20,000 is required in order to purchase 5-10 bonds with different maturities for a specific timeline.