- adjacent interior angle: the angle in a triangle that shares a vertex with the exterior angle
- base: the side opposite the vertex angle
- base angles: the two angles opposite the two sides of equal length
- congruence shortcuts: SSS, SAS, ASA, SAA
- CPCTC: Corresponding Parts of Congruent Triangles are Congruent
- exterior angle: the angle formed when extending one side of a triangle beyond its vertex
- flowchart proof: a logical argument presented in flowchart form
- included angle: and angle included between two sides of a triangle
- included side: a side included between two sides of a triangle
- isosceles triangle: a triangle that has at least two congruent sides
- legs: the two congruent sides
- not congruence shortcuts: SSA, AAA, non-corresponding parts
- pair of remote interior angles: the two angles in a triangle that do not share a vertex with the exterior angle
- paragraph proof: a logical argument presented in paragraph form
- vertex angle: the angle between the two sides of equal length