A wave can be considered as a mean that helps the energy to travel from one point to another. Waves can be classified with respect to their characteristics, such as the direction of movement of particles of medium. Hence, according to waves characteristics, there exists several types of waves: transverse waves; longitudinal waves, mechanical waves and electromagnetic waves.
The most encountered waves are transverse waves, such as water waves or electromagnetic waves. The characteristic of these waves is that the particles of medium oscillate perpendicular to the direction of propagation of waves.
Longitudinal waves, such as sound waves, are characterized by the fact that particles of medium oscillate along the direction of propagation of waves.
Mechanical waves need a medium for they to travel, since this type of waves can travel when medium particles transfer their energies between them, by means of collisions.
Unlike mechanical waves, electromagnetic waves do not need a medium to support the wave displacement. Usually, electromagnetic waves travel in fields generated by charged particles, such as magnetic or electrical fields.
Waves are described by means of their properties, such as: frequency, amplitude, period, wavelength, speed, phase.