From Teflpedia
Disambiguation: Word frequency.

Frequency (/fri:kwənsi/) is a circumstance that refers to how many times something happens within a given period of time. There are two types of frequency; definite frequency and indefinite frequency. In English, frequency is expressed using frequency adverbials, such as adverbs of frequency.

How often is used as a question word.

See also: time, distance, size, etc.