Assets Under Management
  
It's the amount of dough the money manager manages. Why does it matter? Because the fees that the manager earns are based on the size of those assets.
And the public market investing business really scales...that is, if a company is managing 20 billion dollars and has 40 analysts and employees and charges 1% average fee, they are charging $200 million a year to manage that money. Then the market goes up and some more money comes in and a year later, they're managing 30 billion. Their fee might go down to 0.9% on that next 10 billion so the average fee income might be like a shade under $300 million. And yet they still have 40 analysts and employees. HUGELY more profitable, the more assets there are under management.
Nice work if you can get it...and are good at it.