Clipping and masking allow you to subtract portions of elements in an SVG document.
Clipping paths, implemented with the clipPath element, use any combination of paths, text elements, and basic shapes to serve as the outline of a simple mask. This means that everything on the inside of the clipPath element's outline is visible and everything on the outside is cropped out. Every pixel in clipPath is either on or off.
Masks, implemented with the mask element, can contain graphics, text, and basic shapes to serve as a semi-transparent mask. With a mask, each pixel value indicates the degree of opacity and can range from being fully transparent to fully opaque.