Frequency comb is a technique used in precision measurement that involves generating a series of evenly spaced, narrowband laser frequencies known as "comb lines." These comb lines act as a ruler for measuring the frequency of light or other electromagnetic radiation with extremely high precision. Frequency combs have revolutionized fields such as optical spectroscopy, atomic clocks, and telecommunications by enabling accurate and stable frequency measurements over a broad range of wavelengths. They are generated using a variety of methods, including mode-locked lasers and microresonators.