Assets Under Management (AUM) is the total market value of all the investments that a financial institution, like a mutual fund or a hedge fund, manages on behalf of its clients. It's a key metric for measuring the size and success of an investment firm. Essentially, it represents the total amount of money that clients have entrusted to the firm to manage. AUM can fluctuate based on market performance, new investments, and withdrawals. Higher AUM typically translates to higher revenue for the firm through management fees.