Dynamic Frequency Selection (DFS) is a technique used by radio transmitters to avoid transmission in channels that are already occupied. The radio transmitter periodically monitors its local radio environment and notes channels that are occupied. Based on this information the transmitters selects an operating frequency that is not yet used to avoid interference. DFS is a form of Adaptive Frequency Agility (AFA).
DFS can be very useful if a frequency band has to be shared among a large group of users or if the band has to be shared with another service which has a higher priority.
DFS is e.g. used in cordless telephones (DECT) to find a channel that is not occupied by another telephone and by Radio LANs operating in the 5 GHz band to avoid interference in radar systems that use the same frequency band.