Introduction:
The term "virus" refers to a small infectious agent that can replicate only inside the living cells of organisms. The origin of the term is a topic of debate among scientists and historians.

Louis Pasteur:
According to the NCERT textbook, Louis Pasteur, a French microbiologist, was the first to use the term "virus" in the 1890s. He used the term to describe the infectious agent that causes rabies, a deadly disease that affects the nervous system of humans and animals.

Martinus Beijerinck:
However, many scientists believe that Martinus Beijerinck, a Dutch microbiologist, coined the term "virus" in 1898. Beijerinck was studying tobacco mosaic disease, a viral infection that affects tobacco plants. He observed that the infectious agent was smaller than bacteria and could not be seen under a microscope. He called the agent a "contagious living fluid" and later changed the name to "virus," which means "poison" in Latin.

Conclusion:
In conclusion, while the origin of the term "virus" is still debated, both Louis Pasteur and Martinus Beijerinck played important roles in the early study of viruses. Pasteur identified the virus that causes rabies, while Beijerinck discovered the first virus that infects plants. Their work laid the foundation for the modern study of virology, which has led to the development of vaccines and antiviral drugs that have saved countless lives.