See Inside! Makes a new variable when you click on it. It's actually just a "set [variable] to (value)" block which is inside a hidden define block. Because it is hidden, the variable does not get registered until it is ran (And also you need to go out of the code editor or in another sprite then come back to see the new variable. In scratch two it was possible to create a version where you could write the name of the variable you wanted. Then scratch 3 came and removed writable square inputs (fields) so you can't choose a name anymore.
