Viruses are

Viruses are obligate, intracellular, acellular parasites.

Obligate: Viruses are obligate parasites, which means they are entirely dependent on the cellular machinery of a host organism (typically a living cell) for their replication and propagation. They cannot reproduce or carry out metabolic functions independently; they rely on the host cell to replicate and produce new virus particles.

Intracellular: Viruses exist and replicate inside the host cell, taking control of the cellular machinery to produce more virus particles. This intracellular nature is a defining characteristic of viruses.

Acellular: Viruses are not considered living organisms because they lack the cellular structure found in bacteria, plants, animals, and other living organisms. Instead, they are composed of genetic material (either DNA or RNA) enclosed in a protein coat called a capsid. Some viruses may also have additional structures like an envelope.

Parasites: Viruses are parasites because they derive their energy and resources from the host cell, often causing harm or disease to the host in the process.