What is the definition of a virus?

The definition of a virus is accurately described as a parasitic submicroscopic particle. Viruses are unique entities that cannot be classified as living organisms because they lack the cellular structure and metabolic processes typical of living cells. Instead, they consist of genetic material, either DNA or RNA, encased in a protein coat, and, in some cases, an outer lipid envelope.

Viruses rely on a host cell to replicate and reproduce, making them obligate parasites. This parasitic nature underscores their dependence on infecting living organisms. Once inside a host, they hijack the host's cellular machinery to produce new viral particles, illustrating how they operate at a submicroscopic level, which sets them apart from larger, cellular microorganisms.

The other options, including a living organism, a form of bacteria, and an antibody, do not accurately reflect the characteristics of viruses. They do not possess the attributes of life as defined by biological standards, are not classified as bacteria, and are unrelated to antibodies, which are proteins produced by the immune system to identify and neutralize pathogens.