An item designed primarily for the conduction of radio frequency energy, and consisting of two or more conductors supported in fixed spatial relationship(s) along their own length. since the characteristic impedance of the line is determined by the spatial relationships of the conductors, which are sufficiently rigid to maintain these relationships between supports, the configuration of the item is usually not susceptible to mechanical manipulation; that is, it is not normally flexible. includes a single conductor inclosed in an outer concentric conductor (coaxial) or two or more conductors laid parallel. all types have low loss or special characteristics at high frequencies. may include fittings or terminations. for items having continuous homogeneous dielectric, see cable, radio frequency. see also line section, radio frequency transmission.