Rule 144 is the exemption that lets restricted-stock be resold: it requires a holding period, current public information, volume limits for affiliates, and this notice above a small threshold. The volume cap is the greater of 1% of shares outstanding or the average weekly volume over the prior four weeks, per rolling three-month period.
Because it is filed before the sale, a 144 is a forward-looking signal in a way a form-4 is not, though the sale need not actually happen.
Example: 240M shares outstanding gives a 1% cap of 2.4M shares per three months. Average weekly volume is 3.1M, so the affiliate may sell up to 3.1M shares and files a 144 naming that amount.
Related: restricted-stock, form-4, lock-up-period, private-placement, insider-trading