The strength of Java 8 is the introduction of Lambda expression like the strength of Java 5 is annotations.
1. What is Lambda?
Lambda, represented as 
is the 11th letter in in the Greek alphabet and having a value of 30 in Greek numerals. Lambda is used by every science and technology to represent something like lambda particle is sub atomic particle, in crystal optics to represent the period of lattice, in chemistry lambda is an isomer, to represent wave length in optical fiber etc.
Lambda refers anonymous function in a programming language. See the following JavaScript function to know what is an anonymous function.
var price = function (k) { };
The function (function is keyword in JavaScript) does not have a name (like function getMe(k)). This is anonymous function or this is Lambda function. The lambda function does not bind with a name (nameless).
From JDK 1.8, Java allows you to create Lambda functions. Lambda functions will become a powerful concept once integrated with Java.
2. What is Lambda function?
Lambda function, generally known as Lambda expression, is a function but without a name. It is very much used in languages like Python and Ruby (which borrowed from LISP) etc. Now in JDK 1.8, designers are interested to introduce in Java. An anonymous function (lambda function) does not carry name, access specifier, access modifier, parameters etc.
3. Why lambda is required in Java?
It is just to simplify the code. Lambda function is very convenient to use in the same place where we write a function. If you would like to use the function only once, lambda function is the more convenient way. It reduces typing of much code. Because the function code is written directly where we use the function, the programmer need not go another part of application to see the function code (if required to modify).
4. What is the symbol we use?
To write lambda function in Java, we use -> symbol.
5. Where we use Lambda functions?
Lambda function code must be designed to be very short, else, difficult to read. Lambda function can be used anywhere you would like to use a normal function. It is more convenient where a function contains a single statement.
6. Can we avoid Lambda functions completely?
Yes, we can. Using them is never compulsory. Did not Java survive without lambda up to JDK 1.7? It is just stylish. Instead of Lambda, you can use a regular normal function.
Code for using Lambda in Java program refer: JDK 1.8 Features.
