The length from one peak to the next or from any point to the next matching point of a periodic function. Elements in the same period all have the same highest unexcited electron energy level or same ground state energy level. In chemistry the term period refers to a horizontal row of the periodic table.
When large numbers are separated into periods they are easier to read.
As the frequency of a wave increases the time period of the wave decreases. A function f is said to be periodic if for some nonzero constant P it is the case that for all values of x in the domain. The unit for time period is seconds. 2 a 1.