What are lambda functions in Python?

Lambda functions in Python are defined using the 'lambda' keyword and are a way to create small, anonymous functions in a concise manner. They can take any number of arguments but are limited to a single expression. The primary use case for lambda functions is when you need a function for a short period and do not want to formally define it using the standard 'def' keyword, which requires a function name.

For instance, a lambda function can be used in scenarios such as sorting a list of tuples by a specific element or using it with functions like map(), filter(), or reduce(). An example of a lambda function would be lambda x: x + 2, which takes an input x and returns x plus 2.

The other descriptions do not capture the essence of what lambda functions are. They are not defined using the 'def' keyword nor do they have names. Furthermore, they can accept parameters, so the description of regular functions with no parameters does not apply.