Masking and clipping paths each provide a means of selectively revealing content. By using the mask element, you can create subtle blends between masked content and non-masked content. The clipPath element, on the other hand, provides a method of cropping content according to the definition of its enclosed path. The use of either depends solely on the effect you're trying to accomplish; when you need to hide particular elements of your artwork, you can assess which option will serve you best.
With masking and clipping fresh in your mind, you'll move into one of the most challenging and exciting aspects of SVG: filter effects. The next hour will introduce you to filter effects, how to apply them, how to combine them, and more.