Expendable Trust Funds are where funds are allowed to be expended from both principal and interest. An example would be a small scholarship given to the school district for a particular purpose where the total gift would be given, including any interest that may have been received during the time the school district had it in their account.
Non-expendable Trust Funds are those types of scholarship funds that allow only the interest to be spent. Therefore, the principal becomes non- expendable for the school district.