Virus - Wikipedia
Viruses are considered by some biologists to be a life form, because they carry genetic material, reproduce, and evolve through natural selection, although they lack some key characteristics, such as cell structure, that are generally considered necessary criteria for defining life.

Virus | Definition, Structure, & Facts | Britannica
Virus, infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. Viruses possess unique infective properties and thus often cause disease in host organisms.

Viruses: Definition, Types, Characteristics & Facts
A virus is a small piece of genetic information in a “carrying case” — a protective coating called a capsid. Viruses aren’t made up of cells, so they don’t have all the equipment that cells do to make more copies of themselves.

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The Science Behind Viral Infections: How Viruses Hijack the Body
A virus cannot carry out any metabolic processes on its own—no breathing, no digestion, and certainly no movement. Instead, viruses are made up of just a few components: genetic material (either DNA or RNA) encased in a protein coat, sometimes with an outer lipid envelope.

Viral Infection: Causes, Symptoms, Tests & Treatment
What is a virus? A virus is a type of germ (pathogen) that’s so small, you can only see it under a microscope. All viruses carry a small piece of genetic information (DNA or RNA) inside a protective coating (capsid). You can think of it like an envelope carrying instructions.

What Is a Virus? Definition, Structure, and How Viruses Work
A virus is a microscopic infectious agent composed of genetic material—either DNA or RNA—enclosed within a protein coat known as a capsid. Some viruses also possess an outer lipid envelope derived from the host cell membrane.

VIRUS Definition & Meaning - Merriam-Webster
Viruses differ from bacteria in several important ways. Viruses are not living organisms; they can only replicate in the cells of a host. By contrast, bacteria are single-celled organisms that can reproduce on their own and are many times larger than viruses.

Virus - National Human Genome Research Institute
A virus is an infectious microbe consisting of a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat. A virus cannot replicate alone; instead, it must infect cells and use components of the host cell to make copies of itself.

Virology - Wikipedia
Gamma phage, an example of virus particles (visualised by electron microscopy) Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases ...