The term 'isosceles' is a type of triangle that has two sides of EQUAL length. It is derived from the Greek words 'iso' meaning 'EQUAL' and 'skelos' meaning 'LEG'. This type of triangle is one of the most commonly studied shapes in geometry, and is used to teach basic concepts such as angles, area, and perimeter. Isosceles triangles are also used in many practical applications, such as construction and engineering.