What is propriety deal flow?

Proprietary deal flow refers to the source of an acquisition (or mergers and acquisition, M&A) opportunity. Corporate development executives and investment bankers generate "deal flow" for their employers or clients. Deal flow just means the number and quality of acquisition or investment opportunities that a business can consider. Leadership teams know that they will invest in a fraction of the deals they see and a fraction of the ones they invest in will success, so the more opportunities they can examine the better the chance of a good investment decision. Most deal flow comes from sell-side investment bankers trying to attract multiple bidders for a single investment or acquisition. Bidding on these deals tends to be expensive and rushed if the investment banker is doing his or her job. "Proprietary deal flow" just means that the prospective buyer found the opportunity and is the only suitor for the investment. These deals proceed at their own pace and valuations can be (but are not necessarily) more reasonable.