The ownership of a sufficient number of stocks by one stockholder or a company in order to obtain a control/ controlling interest in the issuing company (a publicly traded company).  The stockholder (s) will hold either a majority of the outstanding shares or a significant amount whereby a controlling influence can be exerted on the management of its operations.

A control stock often refers to stock that is associated with voting rights rather than otherwise. In which case, it constitutes the shareholdings of one investors or more that effectively control the issuing company.