What is efficient frontier？

Efficient frontier is a graphical representation of the set of portfolios that offer the highest expected return for a given level of risk, or the lowest level of risk for a given level of expected return. It is a concept used in modern portfolio theory to help investors optimize their portfolios by selecting the best possible combination of assets that will provide the highest return for a given level of risk. The efficient frontier is typically depicted as a curve on a graph, with risk on the x-axis and return on the y-axis. The portfolios that lie on the efficient frontier are considered to be the most efficient and offer the highest return for a given level of risk.