Definition of Lock-up Period
The Lock-up Period is the period of time that certain stockholders agree to waive their right to sell a public company's shares.
Investment banks that underwrite initial public offerings generally insist upon lockups of at least 180 days from large shareholders (i.e. those who have 1% ownership or more).
The goal of a lock-up period is to facilitate market trading. Without a lockup period, management, directors of the company, strategic partners other large investors might sell their stock quickly, to the detriment of new shareholders. If a shareholder tries to sell shares that are subject to lockup during the lockup period, the sale will not be completed.