For a Mutual Fund, it is the fund’s assets less its liabilities. This is divided by the total number of units the fund has issued to investors to determine the NAV per unit. The NAV is declared by the fund at the end of each trading day, based on closing prices of shares and bonds that it owns. One of the things that is reduced to arrive at the NAV is the Total Expense Ratio (TER), the amount that the fund charges you for managing your money.