Underwound DNA, also known as negatively supercoiled DNA, refers to the twisted structure of DNA that has fewer turns than its relaxed state. This structural alteration is crucial for many biological functions like DNA replication, transcription, and DNA packaging. There are a few synonyms for underwound DNA, including incomplete turn DNA, twisted DNA, and negatively coiled DNA. Underwound DNA plays an essential role in maintaining the integrity of the genetic information carried by the DNA molecule. Any disruption in its structure can lead to mutations, genomic instability, and diseases like cancer. Understanding the biology of underwound DNA is of great importance for advancing biomedical research and developing targeted therapies to treat genetic disorders.