Low frequency refers to the portion of the sound spectrum in the lower range, typically covering frequencies from around 20Hz to 200Hz. It corresponds to what we commonly call "bass" and serves as the "foundation" and source of "atmosphere" in sound. Physically, low-frequency waves have long wavelengths, high energy, and strong penetration, but weak directionality. As a result, we tend to "feel" its vibrations more through our bodies (such as the chest and eardrums) rather than simply "locating" it with our ears.
For listening experience and purchasing decisions, low frequency determines the thickness, power, and immersion of sound. A healthy low frequency should "dive deep, be elastic, and respond quickly," clearly distinguishing drum hits from bass lines rather than producing a blurred "humming" sound. When choosing headphones, if you prefer pop, electronic, or movie soundtracks, pay attention to bass quantity and transient response; however, if you seek the purity of classical music or vocals, be cautious that excessive bass may mask mid and high-frequency details, resulting in a muffled sound.
Practical tip: During a trial listen, use a track with continuous bass lines and drum hits, set the volume to a moderate level, and if the low frequency gives you a sense of "heartbeat resonance" without masking vocal and instrument details, then that low-frequency performance is right for you.