Definition of 'Overlay'
A management style that harmonizes an investor's separately managed accounts, preventing the formation of inefficiencies. Overlay management uses software to track an investor's combined position from the separate accounts. Any possible portfolio adjustments will be analyzed by the overlay system, which ensures the overall portfolio will remain in balance and prevent any inefficient transactions from occurring.
Investopedia explains 'Overlay'
When an investor has separately managed portfolios, that investor is placing assets under the control of different managers. This can cause inefficiencies if the managers begin making transactions that either increase the risk of the overall portfolio, have negative tax effects, or unbalance the investor's positions.
For example, if one of the separately managed account traders purchases an asset and another trader sells it, the investor will be left with a neutral position and two transaction fees. Overlay management seeks to improve the communication between the separate managers, allowing for increases in transaction efficiency.