Viruses are acellular organisms that have puzzled scientists regarding their status as living or non-living. The word virus means venom or poisonous fluid. They are described as non-cellular organisms characterised by having an inert crystalline structure outside the living cell.

Several arguments support the view that viruses are non-living. W.M. Stanley (1935) demonstrated that viruses could be crystallised and these crystals consist largely of proteins. Outside their specific host cell, viruses are inert and show no signs of life. They do not possess a cell structure, which is a fundamental characteristic of living organisms. In the five kingdom classification of Whittaker, viruses find no place as they are not considered truly 'living'.

However, viruses also exhibit characteristics of living organisms. Once they infect a cell, they take over the machinery of the host cell to replicate themselves, killing the host. M.W. Beijerinck named the pathogen "virus" and called it Contagium vivum fluidum (infectious living fluid). They are obligate parasites that depend entirely on host cells for their reproduction.

The debate continues as viruses exhibit properties of both living and non-living entities. They are inert outside the host but become active and replicate inside living cells.

In conclusion, viruses occupy a position on the borderline between living and non-living. They are not considered truly living if we understand living as organisms with a cell structure, yet they demonstrate life-like activities when inside a host.