Cyclic DNA refers to a closed circular structure of DNA which is found in certain bacteria and viruses. Some synonyms for cyclic DNA include circular DNA, circularized DNA, double-stranded circular DNA, and closed-circular DNA. A related type of DNA structure is the plasmid DNA, which is a small, circular, double-stranded piece of DNA that is separate from the chromosomal DNA and can replicate independently. Other variations of cyclic DNA include single-stranded circular DNA and linear circular DNA. Studying the properties and functions of cyclic DNA is important in understanding the genetics and evolution of various organisms.