right-click, save as. Refers to the "Save As..." contextual menu item that typically appears when right-clicking on an image or link in a web browser. Used often on message boards when instructing other users that simply viewing a link in your browser will not work, or when someone finds a picture/link so funny that they save it locally for easy access.
neo7784: yo chk out this vid I made rcsa
poster1: lol fecking owls (inserts O RLY pic)
poster2: roffles rcsa