A blockade was the general term for a military action designed to prevent supplies from reaching an enemy via an outside source. On a planetary level, nautical warships could prevent aquatic cargo ships from delivering goods to coastal regions; often this required a large number of warships.
On a much larger scale, starfleets could be used to establish a blockade around a planet to prevent supply vessels from coming and going. The act of a planetary blockade typically included cutting off the targeted world's means of offplanet communications, either through signal jamming or destruction of HoloNet transceivers; though the former was possible on small, backwater worlds, the latter was the usual course of action as planetwide signal jamming was a very difficult feat to pull of on highly-populated worlds. Planetary blockades usually required numerous task-specific warships as well.
Even the most effective blockades had to deal with the occasional smuggling vessels, though depending on the nature of the blockade any such ships that were intercepted could be either forcibly turned back or simply destroyed on sight. Some smugglers, like Han Solo, were particularly skilled at running blockades.