"Duo decimal" is a term that refers to a base-12 numbering system, also known as the duodecimal system. This system was once commonly used in many cultures, but has largely been replaced by the decimal system we use today. Synonyms for the term include "twelve-based," "dozenal," and "duodecimal." Other related terms include "base-12" and "unary dozenal." While this system may not be commonly used, it can be interesting to learn about and may be useful in certain contexts such as music theory or computer programming.