Terminology and abbreviations
Cell fusion	A process of merging two or more cells into one by merging their plasma membranes.
Fusogen	An agent, often a protein such as SARS-CoV-2 spike, capable of fusing cellular membranes. Viral fusogens fuse the viral envelope to the plasma membrane of the target cell and can fuse plasma membranes of adjacent cells to each other.
Syncytium ( plural  syncytia)	A multinucleated cell produced by the fusion of two or more cells. The term comes from Greek syn “together” and kytos “box, or cell”.
Heterokaryon	A syncytium produced from more than one cell type, say, a pneumocyte fused to an epithelial progenitor or a leukocyte.
Homokaryon	A syncytium produced from cells of the same type, as would be the case with the fusion of two or more pneumocytes.
Cell hybrid	Mononuclear offspring of syncytia, produced once a syncytium undergoes mitosis. For example, hybridomas are made by fusing leukocytes with plasmacytoma cells to obtain hybrids that produce monoclonal antibodies.
PS (phosphatidylserine)	The most abundant anionic (negatively charged) membrane lipid. In live cells, PS is actively moved to the cytoplasmic side of plasma membrane.
Scramblases	Proteins, such as TMEM16F, that randomize, or scramble, the asymmetric distribution of PS across the membrane, a process known as  PS externalization .