An antenna or aerial is an electronic device designed to send or receive signals that have specific frequency. Some electronic devices like radio, television, radar, wireless LAN need antennas to work. Antennas work properly in air or outer space. Antenna's length is usually up to the wavelength it uses.
The word 'antenna' is from Guglielmo Marconi's test with wireless equipment in 1895. For the test, He used a 2.5 meter long pole antenna with a tent pole called ' l'antenna centrale ' in Italian. So his antenna was simply called ' l'antenna '. After that, the term 'antenna' became popular among people and had the meaning it has today.
There are many antenna models and each antenna has different purpose. For example, The isotropic radiator is a imaginary antenna that sends signals equally in all directions. The dipole antenna is simply two wires with one end of each wire connected to the radio and the other end hanging free in space. The Horn is used where high gain is needed, the wavelength is short.