Frequency is how often something happens within a certain amount of time. If lightning strikes three times in one minute, that's a higher frequency than lightning striking three times in an hour.

Scientists measure the frequency of ocean waves, earthquakes, and sound waves. Radio stations broadcast at different frequencies: when you tune to 101.5 FM, you're selecting that station's specific frequency. Musicians care about frequency too: a note with a higher frequency sounds higher in pitch, while a note with a lower frequency sounds deeper.

In everyday conversation, frequency describes patterns: the frequency of your dentist visits (hopefully twice a year), the frequency of pop quizzes in math class (maybe once a week), or the frequency of family dinners together. When something happens with high frequency, it occurs often. When something happens with low frequency, it's rare.

The related adjective is frequent, describing something that happens often. You might be a frequent visitor to the library if you go there several times a week. The opposite, infrequent, describes something that happens rarely or seldom.