Triangles

circumcenter

circumcenter

intersection of all perpendicular bisectors of a triangle, equal distance from the vertices

incenter

intersection of all angle bisectors of a triangle, equal distance from the sides

centroid

intersection of all medians of a triangle, divided each median into 2 parts so the distance from the vertex to the centroid is twice the distance from the centroid to the median of the opp side, center of gravity

orthocenter

intersection of all altitudes of a triangle

circumscribed circle

circumcenter

altitude

a line through the vertex that is perpendicular to the opposite side, all altitudes of a triangle are congruent