Efficient frontier
The set of portfolios offering the highest expected return for each level of risk.
The efficient frontier plots the best available trade-off between risk and return. Portfolios below it are inefficient; the policy's chosen point on it reflects the family's risk capacity and risk tolerance.
The frontier is a useful idea with a caveat: it is only as good as the uncertain assumptions behind it. Use it to understand the trade-off between risk and return, not as a precise optimiser whose every decimal should be trusted.