Periodicity

A function is periodic if there is a number such that for every integer . The number is called the period.

If the period is measured in seconds, the frequency is in "Hertz", where 1 HZ = 1. This is the complete cycles per second

In engineering, it is common to use to denote frequency, while physicists tend to use (nu) instead.

Which has the units radians per second. Sometimes, "frequency" means "angular frequency" because of laziness, so watch out.