Blending these asset categories produces bowed lines between them showing more efficient portfolios.

FORBES: Asset Allocation and the Efficient Frontier

In finance parlance and first described by Markowitz, this is an improved efficient frontier for portfolios: higher expected return for a given level of volatility, or lower volatility for a given level of expected return.

FORBES: The Multiple Rewards of Multi-Asset-Class Investing

The efficient frontier is a continuum of portfolios made up of investments along the upper left edge.

FORBES: The Efficient Frontier