Anonymous functions, also known as lambda functions, are functions that do not have a name. They are often used for short, simple operations where defining a full function would be unnecessary. In programming languages like Python and JavaScript, anonymous functions can be created on the fly and passed as arguments to other functions, making them useful for tasks like sorting or filtering data. These functions are typically defined using a concise syntax, allowing for quick implementation. Because they lack a name, they are often used in situations where the function is only needed temporarily, helping to keep the code clean and readable.