Viruses are not cells. They lack the fundamental components that define a cell, such as a cell membrane, cytoplasm, and organelles. Instead, viruses are much simpler structures consisting of a protein coat called a capsid that encloses their genetic material (either DNA or RNA).
Viruses are not considered "alive" because they cannot replicate on their own. They rely on infecting host cells and using the host's cellular machinery to make copies of themselves.
Think of a virus as a tiny package of instructions that hijacks a cell's machinery to produce more virus particles. This process often results in the death of the host cell, as the virus replicates and spreads.