About Variable
A variable is a container holding information. And the content can be different. By changing the value of a variable as the movie plays, you can record and save information about what the user has done, record values that change as the movie plays, or evaluate whether a condition is true or false.
Variables can hold any type of data: number, string, Boolean, object, or movie clip. The type of data a variable contains affects how the variable’s value changes when it is assigned in a script.
Variables:
Math, System, Date, _root, _level