Its unit is meter, being the dimension of length. Time period of a wave is the time it takes to complete one cycle of motion. Its unit is second. Frequency is defined as number of waves produced in one second. Waves are generally produced by disturbance in a medium.
Examples are water waves and light waves.
Longitudinal waves are those which travel in the same direction as its displacement. Example is sound wave. If the light source is extended in a plane, light pulses are like traveling plane surfaces. These imaginary surfaces are called Wave fronts. Any point on the wave front has the same physical property as another point on the same wave front.