Acute triangle
A triangle whose angles are acute.

Altitude
Height

Altitude of a triangle
The perpendicular segment from a vertex to the line containing the opposite side of a triangle.

Angle bisector
A ray that is in the interior of an angle and forms two equal angles with the sides of that angle.

CPCTC

Corresponding Parts of Congruent Triangles are Congruent.

Equilateral triangle
A triangle whose sides are equal in length.

Isosceles triangle
A triangle with two sides of equal length.

Median
The segment connecting the vertex of an angle in a triangle to the midpoint of the side opposite it.

Obtuse triangle
A triangle with one acute angle.

Perpendicular bisector
The bisector of a segment perpendicular to it.

Right triangle
A triangle that has a 90 degree angle.

Scalene triangle
A triangle with no equilateral sides.

Triangle
A polygon with three sides.