Transversal wave

A transverse wave is a moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer (or the propagation of the wave).

If a transverse wave is moving in the positive x-direction, its oscillations are in up and down directions that lie in the y–z plane.

Light is an example of a transverse wave, while sound is a longitudinal wave. A ripple in a pond and a wave on a string are easily visualized as transverse waves.

Transverse waves are waves that are oscillating perpendicularly to the direction of propagation. If you anchor one end of a ribbon or string and hold the other end in your hand, you can create transverse waves by moving your hand up and down. Notice though, that you can also launch waves by moving your hand side-to-side. This is an important point. There are two independent directions in which wave motion can occur. In this case, these motions are the y and z directions mentioned above, while the wave propagates away in the x direction.

Continuing with the string example, if you move your hand in a clockwise circle, you will launch waves in the form of a left-handed helix as they propagate away. Similarly, if you move your hand in a counter-clockwise circle, a right-handed helix will form. These phenomena of simultaneous motion in two directions go beyond the kinds of waves we observe on the surface of water - in that a wave on a string can be two-dimensional.

Two-dimensional transverse waves exhibit a phenomenon called polarization. A wave produced by moving your hand in a straight line, up and down for instance, is a linearly polarized wave, a special case. A wave produced by moving your hand in a circle or an ellipse is a circularly or elliptically polarized wave, two other special cases.

Electromagnetic waves behave in this same way, although it is slightly harder to see. Electromagnetic waves are also two-dimensional transverse waves.

Ray theory does not describe phenomena such as interference and diffraction, which require wave theory (involving the phase of the wave). You can think of a ray of light, in optics, as an idealized narrow beam of electromagnetic radiation. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing. A light ray is a line or curve that is perpendicular to the light's wavefronts (and is therefore collinear with the wave vector). Light rays bend at the interface between two dissimilar media and may be curved in a medium in which the refractive index changes. Geometric optics describes how rays propagate through an optical system.

...
Wikipedia