The predetermined amount of time that stockholders have agreed to waive their right to sell their shares of a public company. Investment banks that underwrite initial public offerings generally insist upon lockups of at least 180 days from large shareholders in order to allow an orderly market to develop in the shares. The shareholders that are subject to lockup usually include the management and directors of the company, strategic partners and such large investors. These shareholders have typically invested prior to the IPO at a significantly lower price to that offered to the public and therefore stand to gain considerable profits. If a shareholder attempts to sell shares that are subject to lockup during the lockup period, the transfer agent will not permit the sale to be completed.