What is Assets Under Management (AUM)?

Assets under management (AUM) is a measurement used to signify the total market value of all assets being managed by a financial fund, institution, or portfolio manager. However, the exact definition of what AUM constitutes is ambiguous because not all institutions classify different types of assets in the same manner. The AUM value fluctuates due to regular market movements and because of money inflows and outflows to and from the fund.