 A variable is a container that you can store a value in. When you use that variable in an algorithm, it opens up the container and looks at the value inside. This lets you write smarter algorithms that behave differently depending on the value stored in the variable. For example, if you wanted to write an algorithm to say, happy birthday, you're turning 10 to my little brother, that's great now. But when I run it next year, I'd want it to say, happy birthday, you're turning 11. I could create a variable called age to store my brother's age and write my algorithm that say, happy birthday, you're turning age instead, because variables can change. Each year, I can update the variable age to equal age plus 1. Now you're going to try a play lab where you are given different games and you can change the values of variables like speed, height, score in order to change the game. You won't have to change the algorithm of the game to change how it plays, just the variable. In my work for Kindle and on X-ray for Books, we apply variables in many different ways. One way that you can use a variable is to store page numbers of a book. A user can increase and decrease the size of the font in the page. Based on the font size, the number of pages in the book can change. We can adjust it by storing the page numbers in a variable.