Fn

Fn, short for function, is a common abbreviation used across mathematics, computer science, and computing hardware. In mathematics, a function is a rule that assigns to each input from a domain exactly one output in a codomain. It is typically denoted by letters such as f, with expressions like f(x) representing the output corresponding to the input x.

In programming, fn or function denotes a construct for defining a function. The exact syntax depends on the language. A notable example is Rust, which uses the keyword fn to declare functions, for instance: fn add(a: i32, b: i32) -> i32 { a + b }. Rust also uses the term Fn in its type system to describe callable entities, including function items and closures.

In user interfaces and hardware, Fn is common as a label on laptop keyboard keys. The Fn key acts as a modifier to access secondary functions printed on other keys, such as brightness or volume controls.

The use of fn as an abbreviation for function is widespread due to its brevity and clarity, but details vary by field. In general, it signals a concept that takes inputs and produces outputs.