Qualified institutional buyers are the U.S. Institutional investors that under Rule 144A, are allowed to buy securities issued by a non-American issuer. To qualify as a qualified institutional buyer a financial institution must own and manage $100 million ($10 million in the case of a registered Broker-dealer) or more in qualifying securities. For a banking institution to qualify, a $25 million minimum Net worth test must also be satisfied.

(See Chapter 26 Value and corporate finance of the Vernimmen)

To know more about it, look at what we have already written on this subject