The term 'ACE2' refers to Angiotensin-Converting Enzyme 2, which plays a crucial role in the renin-angiotensin system that regulates blood pressure and fluid balance. It has gained prominence in the context of viral diseases, particularly COVID-19, as the spike protein of the SARS-CoV-2 virus binds to ACE2 to enter human cells. Understanding ACE2's function and its interaction with viruses is essential for comprehending the mechanisms of viral entry and the development of therapeutic strategies, thus linking it to the broader scope of viral pathogenesis relevant for UPSC studies.