All of them except for the first one are differences of squares. Differences of squares is a form of factoring perfect squares. A 'perfect square' is just a fancy term that basically means you are doubling a number. Like the number 25 you multiply 5x5 to get that number and if you were to take the square root of that number you would also get 5. For it to be differences of two squares you have to have two numbers that if square rooted (in a calculater if you need one) would turn out to be a whole number or 'perfect'.
