NOTE: From the definitions you can see the differences.
Median:-
Segment joining a vertex to the mid-point of opposite side is called a median. All three medians which are concurrent at a point called the Centroid.
Altitude:-
Perpendicular from a vertex to opposite side is called altitude. All three altitude which are concurrent at a point called the orthocentre.
Perpendicular Bisector:-
A Line which passes through the mid-point of a segment and is perpendicular on the segment is called the perpendicular bisector of the segment. All three perpendicular bisectors which are concurrent at a point called the circumcentre (the centre of the surrounding circles)
