F5

F5 is a designation used in several unrelated fields, including computing, mathematics, music, and industry. It may refer to a function key, a mathematical field, a music pitch, or a technology company.

On keyboards, F5 is a function key in the top row. In many programs it triggers a refresh or reload; in web browsers it reloads the current page, and Ctrl+F5 bypasses the cache. In PowerPoint, F5 starts the slideshow from the beginning.

F5 in mathematics denotes the finite field with five elements, GF(5). It comprises the integers 0 through 4 under addition and multiplication modulo 5 and is used in number theory and coding theory.

In music notation, F5 indicates the F in the fifth octave, typically near 698 hertz under standard concert pitch.

F5 Networks is an American technology company that designs application delivery networking hardware and software. Founded in 1996, it offers products such as BIG-IP for load balancing, application security, and traffic management, along with cloud and security services built on its TMOS operating system.

Historically, F5 has also referred to a tornado rating on the Fujita scale, describing extremely violent storms with winds estimated above 261 mph; this usage has largely been superseded by the Enhanced Fujita scale.