The spike (S) protein of nCoV/SARS-CoV-2/COVID-19 is one of the structural glycoproteins that remains embedded in viral envelope and acts as the fundamental component of early viral infection of nCoV/SARS-CoV-2/COVID-19 upon binding the host receptor. The nCoV/SARS-CoV-2/COVID-19 has a trimeric spike protein which has two main domains such as S1 domain for receptor binding and S2 domain for membrane fusion and several specific cleavage sites in S1- S2 boundary junction that needs a novel, endocytic protease- primed cleavage to get activated during infection. It mainly binds to the furin protein on the cell membrane which performs trypsin like proteolytic cleavage and then the protein gets activated facilitating its entry into the host. This transmembrane spike protein of nCoV/SARS-CoV-2/COVID-19 shares binding property to the Angiotensin Converting Enzyme 2 (ACE2) likely to that of SARS- CoV. The high affinity of nCoV/SARS-CoV-2/COVID-19 Spike protein for human ACE2 may contribute to the apparent ease with which nCoV/SARS-CoV-2/COVID-19 can spread from human-to-human and make nCoV/SARS-CoV-2/COVID-19 pandemic.