Lockup periods prevent post-IPO insider selling for a defined window, typically 90 to 180 days. The lockup gives the public market time to absorb the new stock without the price overhang of insider selling. When the lockup expires, share price often dips temporarily as insiders rebalance.
Lockups apply to founders, employees, and early investors. Some companies arrange staggered or graduated lockup releases to smooth the post-lockup trading impact. SPAC lockups have their own structure tied to the de-SPAC date.