It's trade receivables. According to the Receivables Exchange, $11 trillion of trade receivables is originated by small and mid-size businesses and another $6 trillion by large corporations, for a whopping total market size of $17 trillion.

As US money market funds are squeezed by new regulation, the types of commercial paper (CP) these funds can buy is limited to the top-rated corporations and banks. The smaller or lower rated firms have limited or no access to the CP markets. And banks sometimes have a limited appetite to finance corporate receivables on their balance sheets.

By opening up receivables financing to end-users directly, the exchange effectively creates an alternative to CP or money markets for investors to park their cash. The receivables term tends to be quite short (typically under 2 months), but there is clearly credit risk associated with these transactions. Many of these firms are smaller and/or sub-investment-grade or unrated - so credit work needs to be done prior to investing