What is virus explain the types of virus?

A virus is a microscopic infectious agent that can only replicate inside the living cells of an organism. They are composed of genetic material (either DNA or RNA) encased in a protein coat and sometimes surrounded by a lipid envelope. Viruses can be classified into several types, including DNA viruses (like herpesvirus), RNA viruses (like influenza), retroviruses (which reverse transcribe their RNA into DNA, like HIV), and bacteriophages (viruses that infect bacteria). Each type varies in structure, replication mechanism, and the organisms they infect.