This Instructional Activity is a part of the Lesson 11, Unit 1, Grade 6. Developing a useful and complete definition of a polygon is harder than it seems. A formal definition is often very wordy or hard to parse. Polygons are often referred to as "closed" figures, but if used, this term needs to be defined, as the everyday meaning of "closed" is different than its meaning in a geometric context. This activity prompts students to develop a working definition of polygon that makes sense to them, but that also captures all of the necessary aspects that makes a figure a polygon. Here are some important characteristics of a polygon.