What is the meaning of screen?

(DoD, NATO) In cartography, a sheet of transparent film, glass, or plastic carrying a "ruling" or other regularly repeated pattern which may be used in conjunction with a mask, either photographically or photomechanically, to produce areas of the pattern.
(DoD, NATO) An arrangement of ships, aircraft and/or submarines to protect a main body or convoy.
(DoD) A task to maintain surveillance; provide early warning to the main body; or impede, destroy, and harass enemy reconnaissance within its capability without becoming decisively engaged. See also security operations.
(NATO) A security element whose primary task is to observe, identify, and report information, and which only fights in self-protection. See also flank guard; guard.
(DoD, NATO) In surveillance, camouflage and concealment, any natural or artificial material, opaque to surveillance sensor(s), interposed between the sensor(s) and the object to be camouflaged or concealed. See also concealment.