Median
In a triangle, a line joining the midpoint of a side to the opposite vertex is called a median.
AD is a median of
ABC.

ABC in the following figure.

Altitude
In a triangle, the perpendicular from a vertex to the opposite side is called the Altitude.
In
ABC of the following figure, AD is the altitude.


In Fig.(ii): AB, CB and BD are the altitudes. B is the orthocentre.
In Fig.(iii): Three altitudes AD, BE, CF are produced to meet at O. O lies outside the obtuse angled triangle.In a triangle, the bisectors of the three angles meet at a point called the Incentre.
In
ABC in the figure above, the bisectors of the three angles meet at I. I is the Incentre.
In a triangle, the perpendicular bisectors of the three sides meet at a point called the Circumcentre.
In
ABC, OD, OE, OF are the perpendicular bisectors of sides BC, AC and AB. O is called the circumcentre.
