Hertz (abbreviated: Hz) is the standard unit of measurement used for measuring frequency. Since frequency is measured in cycles per second, one Hertz equals one cycle per second. For example, 30 Hertz means 30 times per second.
Abbreviated Hz and named after Heinrich R. Hertz.
In phones, this often is used to measure how often a display refreshes the images it displays. Although 30 Hz is often fast enough for most situations, 60 Hz can look smoother, and even faster Hz can provide a noticeable benefit when displaying content with very fast motion, such as fast-paced games.