HC stands for High Contrast, that is a rose tinted lens which means that the base color of the lens is rose colored. You might also see the letters LAF, that indicates a Light Amplifying lens, which means the tint is yellow.
HC Rose/red tints are ideal for situations with varied terrain in low light situations. These lenses are ideal for use on snow or in poor weather conditions.
LAF Yellow tints also do well in low light because they brighten everything up by increasing light receptivity. This is great for things like trail running and mountain biking.