Frequency combs are precise optical sources composed of a series of evenly spaced spectral lines. These combs are generated by mode-locked lasers, which produce a train of ultrashort pulses with very stable and well-defined frequencies. Frequency combs have revolutionized a wide range of scientific and technological fields, including precision frequency metrology, spectroscopy, and astronomical observations. They allow for the measurement of frequencies with extremely high precision and accuracy, making them invaluable tools for various applications in physics, chemistry, and engineering.