Days Sales Outstanding: DSO measures how much of a company's credit sales are tied up unproductively as accounts receivable.
The lower the DSO number, the more efficient the company. E.g., a company with an average A/R balance of $640,000 over 30 days and total credit sales of $742,000 for the same period has a DSO of 25.9 days.
DSO measures the efficiency of a company's A/R management. Revenue tied up in receivables cannot be used to fund operations or grow the business.