A wave is an oscillation in energy. In the context of electromagnetic radiation, the electric and magnetic fields oscillate. These oscillations repeat a pattern. For example, think of a sine wave.
It starts at zero, goes up to a crest, goes down to a trough, and comes back to zero. In this figure, the wave is propagating over a distance, so the pattern is called a cycle and the length of the pattern is called the wavelength. Imagine standing in one spot while the wave travels past. The frequency is the number of cycles that pass by in a given time, such as one second. The time it takes one cycle to pass is called the period. For electromagnetic waves, the frequency and wavelength are related by the following equation: where c = λν, is the speed of light.
