What is a variable?

Students are investigating the flight of paper whether it be in the form of a plane or a wad of paper in order to define what a variable is.  After each trial, students are changing the experiment in way to accomplish a goal. When they modified their design, they described these changes in their science notebook.  As the lesson finished, students shared some of the things they did to change their experiment concurrently we agreed that these "changeable things" are called variables.