An unit for measuring frequency?

Frequency is the measure of how frequent something is. It might also

be called "oftenness" because it tells how often something happens.

Its dimension is reciprocal time. So its units could be 'per second',

'per minute', 'per day', etc.

The SI unit of frequency is called the Hertz (Hz).

"1 Hertz" means "1 per second".

Hertz, The word "hertz" is named after Heinrich Rudolf Hertz, who was the first person to prove the existence of electromagnetic waves.