(1) The darkness of a printed image. If the ink or toner is running out in your printer, you will notice that the images it prints are not as dark as they used to be. You can sometimes adjust the density with a dial on the printer, otherwise you will probably need to replace the cartridge. (2) The amount of data that can be stored on a floppy disk; a single-density 3.5-inch disk can store 720Kb of data, while a double-density disk can store 1.44Mb of data.