a line joining the midpoints of two sides of a triangle.

a point that is in three or more lines simultaneously.

The point where the three perpendicular bisectors of the sides of a triangle meet.

a line segment joining a vertex to the midpoint of the opposite side.

The point where the medians of a triangle intersect.

the perpendicular distance from any of its vertices to the opposite side.

The point where the three altitudes meet.