Skeleton-like shape features (i.e., centerlines, medial surfaces, and
topological kernels) are frequently used region-based shape features which
summarize the general form of objects and represent their topological
structures. They play important role in various applications in image
processing, pattern recognition, and visualization. I shall define
skeletons and present their properties. Then the three major
skeletonization techniques will be presented. Finally some applications
will be outlined.