What is an anonymous function in PHP?

An anonymous function in PHP is defined as a function that does not have a specified name. This allows it to be created and used in situations where it might not need a formal name, such as when passing it as a callback function or defining it inline.

Anonymous functions, also referred to as closures, can be particularly useful in scenarios such as array manipulation, where a temporary function needs to be executed on each element of an array. They provide a convenient way to encapsulate functionality without cluttering the global namespace with unnecessary function names.

The concept of having a function that lacks a name allows for more flexible programming paradigms, such as functional programming, where functions can be treated as first-class citizens and passed around like any other type of data.

Other options do not accurately describe an anonymous function. A function with a user-defined name explicitly indicates that it is named, while options referring to callbacks and built-in functions do not capture the essence of what makes an anonymous function unique.