The period of a wave (T) is the time it takes to complete one cycle. It's the inverse of frequency, the number of cycles in a given time. For example, if a wave has a frequency of 10 seconds per second, then its period is 0.1 second because it takes 0.1 seconds for a single cycle. Other quanitites associated with a wave are:

wavelength - the distance between two corresponding parts of a wave, or distance for one complete cycle.

energy - related to frequency and inversely related to wavelength

speed - distance traveled by a wave divided by the elapsed time

Speed is equal to wavelenth times frequency: speed =`lambdanu`

Since period (T) is 1/`nu` , speed equals `lambda` /T

Electromagnetic radiation has a constant speed, c = 3.00 x10^8 m/s, so electromagnetic waves with a longer period will have a longer wavelength and lower energy.