A guyed mast is a tall thin vertical structure that receives support from guy lines.
Guyed masts are frequently used for radio masts. The mast can either support aerials (for VHF and UHF) mounted at its top, or the entire structure itself can function as an antenna (for VLF, LF, MF and HF); this is called a mast radiator. In the latter case, the mast needs to be insulated from the ground. They can also be used to support all types of wire aerials (for VLF, LF, MF and HF).
Sailing masts, the masts that support the sails on sailboats, are very typically guyed masts.
Guyed masts can also be used as the tops of free standing towers. A famous tower of this type is the Gerbrandy Toren.
Guyed masts are sometimes also used for meteorological measurements at certain heights above ground level. Sometimes they are used as pylons, although their usage in agricultural areas is problematic because anchor foundations handicaps ploughing. A very special use is the BREN Tower.
Craning is the act of climbing cranes and include guyed masts. Apart from the danger of falling, microwave radiation from the antennas is an often overlooked danger.