Intensity:
Intensity, in pixel terms, is the shades of colours you can get, the higher the intensity the brighter the colour. The highest intensity is always white, whilst the lowest is black. Using intensities, you can make whats called grey scale pictures.
Gray scale pictures can only use grey (including black and white) intensities to make pictures, using shading to make it stand out and not just look like a scribble There are only 256 intensities of grey to use, even though that's still a lot, combine it with the rest of the pallet, and it's a huge amount of colours at your disposal.