Raster and grid images are special kinds of layers. These are image files plus a registration point TAB file that allows the image to be rendered as a map layer. You can create a registration point file in MapInfo Pro.
A raster is typically a background layer used for reference: aerial photo, topo map, custom graphics. User-controlled properties of raster images include brightness, contrast, opacity, grayscale and transparency.
A grid is an overlay layer that shows a continuous gradation of color to represent interpolated values from the underlying data. User-controlled properties of a grid include brightness, contrast, opacity, grayscale, transparency, and an inflection collection (how the colors are defined and spread).