The resolution at which a device can process an image. Using interpolation, the device assigns intermediate values based on known values to achieve higher resolution than the optical resolution offers.

a meaningless measure - it is what happens when the camera's base resolution is artificially boosted by simply inserting extra pixels that have artificial data sort of midway between the real pixels

Resolution enhanced through software; also known as software-enhanced resolution. For instance, if your optical resolution is 600 x 1200 dpi, you may be able to enhance images up to 9600 x 9600 dpi through software interpolation. During an interpolated scan, the scanner software mathematically creates more pixels using the actual pixels acquired (optical scan) from the scanned document. This synthetic creation of extra pixels can be useful for certain tasks, such as scanning line art or enlarging small originals, as it helps to eliminate pixelization and lends a smoother appearance to the image.