What do we mean when we write "senescence,""apoptosis,""necrosis," or "clearance of dying cells"?

The clearance of dying cells has become an important field of research. Apart from a significant increase in our understanding of the mechanisms for uptake, cell clearance is a basic mechanism in tissue homeostasis, cancer, resolution of inflammation, induction of tolerance, and autoimmunity. Phagocytosis of dying cells is a complex process, involving many interacting molecules on the dying cell and the phagocyte, and in the microenvironment. Although much is known on the subject, there are many questions and unknown variables that remain under investigation. Naturally, different terms were developed, among which some are misused, leading sometimes to pseudoconflicts of understanding. Several receptors were described as "phosphatidylserine receptor: are they all equal?" We will revise terms such as apoptosis, primary and secondary necrosis, lysed cells, senescent cells, clearance of apoptotic cells, efferocytosis, and more. We will try to point out misnomers, misunderstandings, and contradictions, and to define a consensual vocabulary.