Before revision: Equity order flow is persistent in the sense that buy orders tend to be followed by buy orders and sellorders tend to be followed by sell orders. For equity order flow this persistence is extremely long-ranged, with positive correlations spanning thousands of orders, over time intervals of up to several days.
After revision: Equity order flow is persistent in the sense that order signs (to buy or sell) are positively autocorrelated out to time lags of tens of thousands of orders, over time intervals of up to several days.