As per the official documentation:
Visual (8-bit): the visual product is an orthorectified 8-bit GeoTIFF that has a color curve pre-applied in order to be more readily usable in most visual analysis and display applications.
Analytic (12-bit): the analytic product is 12-bit data delivered in a orthorectified 16-bit GeoTIFF file with no visual color-corrections are applied; it is designed for analytical and scientific applications.
Unrectified (12-bit): a 12-bit analytic product without orthorectification applied. Radiometric and flat field corrections are made to the unrectified product to account for radiometric and sensor distortions. Rational Polynomial Coefficients (RPCs) are available to transform unrectified data.