Space denial referred to a strategic and tactical doctrine in use by the Alliance to Restore the Republic during its early years and subsequent to the Battles of Yavin and Endor.
Space denial was a means by which the Rebellion could deny the free movement of Imperial forces within Imperial-controlled space without significant protection, thus it was never meant to take and hold territory. The strategy behind space denial focused on small units of starfighters, usually at the squadron level, operating from hidden bases established near known Imperial supply routes and employing hit-and-run tactics and convoy harassment. Optimally, the goal of the strategy was to take out targets of opportunity and to force the Empire to divert forces away from more heavily-defended sectors, thus diluting overall Imperial naval strength.
Due to the expense of keeping starfighters operational and the lack of resources available to the Alliance in comparison to their enemies, space denial was the only viable alternative to wresting control of space from the Empire. Thus it was used heavily in the early days of the Rebellion and through to the aftermath of the Battle of Endor. Though Emperor Palpatine and Darth Vader were dead and the second Death Star had been destroyed, the Alliance still lacked resources; thus space denial continued to be an effective strategy against the remnants of the Empire.