In Java, what is a lambda expression?

A lambda expression in Java is indeed a concise way to represent an anonymous function. It allows you to define a function without the need to create a full-fledged class or method. This is particularly useful in scenarios where a function is required, such as when using functional programming paradigms and passing behavior as parameters, especially with collections.

Lambda expressions provide a clear and succinct way to express instances of single-method interfaces, often referred to as functional interfaces. For example, instead of creating a separate class that implements an interface with a single method, you can use a lambda expression to define its behavior inline, enhancing code readability and reducing boilerplate code. This feature plays a significant role in stream processing and event handling, making the code cleaner and more maintainable.

The other options do not correctly define what a lambda expression is. The first choice pertains to method parameters, the third is unrelated to function expression and is about random number generation, and the fourth describes a characteristic of data structures rather than a specific function type.