Telecommunication cables are a type of guided transmission medium

Transmission medium

A transmission medium is a material substance that can propagate energy waves...

s. Cables are usually known to transmit electric energy (AC

Alternating current

In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

/DC

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

) but in telecommunications fields, cables are used to transmit electromagnetic waves, they are called electromagnetic wave guides.
Telecommunications are based on transmitting modulated waves/signals through a medium and receiving them. When the distance between the transmitter and receiver is far, or we are using unguided medium transmission, the antennas

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 are used, otherwise in guided medium transmission, the telecommunication cables are used.
Telecommunication cables are divided into several types

• Transmission Line
  Transmission line
  In communications and electronic engineering, a transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that its wave nature must be taken into account...
  
  s when electric signals are transmitted.
• Waveguide
  Waveguide
  A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...
  
  s when electromagnetic waves are transmitted.
• Optical Fiber
  Optical fiber
  An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
  
  s when light signals are transmitted.