In wave motion, period, the time one complete cycle takes, is the reciprocal of this, the no. of cycles in a given time
[DOC] [TLE] Frequency and Period of a Wave - The Physics Classroom [PAR] Given this definition, it is reasonable that the quantity frequency would have units 
of ... Period, being a time, is measured in units of time such as seconds, hours, ... 
it takes the minute hand 3600 seconds to complete one cycle around the clock.