Lock-up provision is a term used in corporate finance which refers to the option granted by a seller to a buyer to purchase a target company’s stock as a prelude to a takeover. The major or controlling shareholder is then effectively "locked-up" and is not free to sell the stock to a party other than the designated party (potential buyer).
Typically, a lockup agreement is required by an acquirer before making a bid and facilitates negotiation progress. Lock-ups can be “soft” (shareholder permitted to terminate if superior offer comes along) or “hard” (unconditional).