A dual frequency comb refers to a type of frequency comb that simultaneously generates two sets of evenly spaced optical frequencies. This means that it can produce two distinct sets of laser light with specific frequencies that are evenly spaced across a broad spectrum. Dual frequency combs are useful in a variety of applications, particularly in precision spectroscopy, frequency metrology, and optical frequency synthesis. They can be used to characterize and control the frequencies of lasers with extremely high precision, making them valuable tools in a wide range of scientific and technological fields.