The document defines and distinguishes between the three types of triangles based on the length of their sides: equilateral triangles have all three sides equal in length, isosceles triangles have two sides of equal length, and scalene triangles have all three sides of different lengths. It provides examples of each type of triangle and asks the reader to identify whether triangles are equilateral, isosceles, or scalene by checking, crossing, or drawing a star next to descriptions.