Depression is really a large group of diseases/conditions just like cancer with a broad range of different forms, except we haven't yet developed any way of con

Depression is really a large group of diseases/conditions just like cancer with a broad range of different forms, except we haven't yet developed any way of conclusively delineating the different forms like we do with leukemia, melanoma, lymphoma, lung cancer, etc. Just like most adults develop some form of cancer - in the form of benign tumors - most adults will experience some form of depression as they age, mostly as short bouts of general sadness. A small but significant fraction, however, will develop forms of depression that are the equivalent of 'metastatic' cancer that are far more serious and threatening. When people talk about "clinical depression," they usually mean the latter group that have qualitatively more serious symptoms like suicidal ideation and extended periods of depression which lead to ongoing negative consequences like trouble forming and maintaining relationships and jobs, sleeping far more than normal, etc.