Is the circumcenter the point shared by the altitude of a triangle?

No, the circumcenter is not the point shared by the altitudes of a triangle; that point is called the orthocenter. The circumcenter is the point where the perpendicular bisectors of the sides of a triangle intersect, and it is the center of the circumcircle. In contrast, the altitudes of a triangle intersect at the orthocenter, which is a different point altogether.