Can you explain what a lambda expression is in programming and how it is used?

A lambda expression in programming is a compact way to describe an anonymous function, that is, a function without a name, which can be passed as a parameter or used for concise code writing.

In C#, lambda expressions are often used to create delegates or LINQ expressions. They have the syntax:

(parameters) => expression

or

(parameters) => { statements }

Example of usage:

// List of numbers
List<int> numbers = new List<int> {1, 2, 3, 4, 5};

// Using lambda to filter even numbers
var evenNumbers = numbers.Where(n => n % 2 == 0);

foreach(var num in evenNumbers)
{
    Console.WriteLine(num); // Will output 2 and 4
}

Here, n => n % 2 == 0 is a lambda expression that takes a parameter n and returns true if the number is even. This allows writing more expressive and concise code.