The risk and efficiency of a portfolio of financial products can not be assessed without a clear and measurable investment goal. The risk of the portfolio is about not achieving that goal.
Efficient portfolios are portfolios that are most likely to be the most effective.
To give an example, let's focus on an investment portfolio that is kept to finance some future projects or obligations. The efficiency of the portfolio depends on the adequacy of its cash flows. In cases, where it is not always possible or too expensive to match the cash in- and outflows perfectly, active management should limit the risk invoked by the mismatch of the cash flows to an acceptable level.