Institutional flows are the biggest component of the market, I believe. There are a lot of pension funds and insurance companies and family endowments, worldwide.
I presume this observation includes mutual funds? In addition, there are hedge funds, which could be institutional investors or individual investors.
If this means a zero flow of funds
The conventional wisdom (I've never seen this proven) is that individual investors always have it wrong. When they are buying stocks, we are closer to the top than the bottom (1999). When they are selling stocks, we are close to the bottom.