Frequency is a part of our common, everyday language. In mathematical terms, the frequency is the number of complete vibrational cycles of a medium per a given amount of time. If a coil of slinky makes 2 vibrational cycles in one second, then the frequency is 2 Hz. If a coil of slinky makes 3 vibrational cycles in one second, then the frequency is 3 Hz. The quantity frequency is often confused with the quantity period.
Period refers to the time which it takes to do something.
When an event occurs repeatedly, then we say that the event is periodic and refer to the time for the event to repeat itself as the period. The period of a wave is the time for a particle on a medium to make one complete vibrational cycle. Period, being a time, is measured in units of time such as seconds, hours, days or years. When a physics teacher is regular with his stools, the period of the stools is 24 hours. Frequency and period are distinctly different, yet related, quantities.