Period and frequency are related - one is the reciprocal of the other.
Period is the number of seconds per wave. Frequency is the number of waves per second.
In other words, the period is how long it takes one cycle of something to occur. The frequency is the number of cycles that occur per unit time, often seconds.
If 5 waves pass a point in a second, the frequency is 5Hz and the period is 0.2s (each wave took 0.2s to pass the point).
