Retroviruses are a type of virus that have RNA as their genetic material. They replicate by converting their RNA into DNA using an enzyme called reverse transcriptase. This DNA then integrates into the host cell's genome, allowing the virus to reproduce and spread within the host. One well-known example of a retrovirus is the HIV virus, which causes AIDS. Retroviruses can infect various organisms, including humans, animals, and plants. They are often associated with certain diseases, but some retroviruses can also be harmless and exist in the genomes of many species without causing illness.