In radio, longwave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths.
In contemporary usage, the term longwave is not defined precisely, and its meaning varies across the world. Most commonly, it refers to radio wavelengths longer than 1000 metres; frequencies less than 300 kilohertz.
The International Telecommunication Union Region 1 longwave broadcast band falls wholly within the low frequency band of the radio spectrum (30–300 kHz).