The cellular catabolic process in which cells digest parts of their own cytoplasm; allows for both recycling of macromolecular constituents under conditions of cellular stress and remodeling the intracellular structure for cell differentiation. [ http://www.ncbi.nlm.nih.gov/pubmed/9412464 https://www.worldcat.org/search?q=bn%3A0198547684 http://www.ncbi.nlm.nih.gov/pubmed/11099404 ]