It is called its bounds. In the case of 2 dimensional objects, it is part of the perimeter.
The outer edge means the furthest most point from the center. The outer edge is usually the end of the object before the dropping off point.
Perimeter
The outer edge of a circle is called the circumference.
Its perimeter
outline
outline
The out edge of a cup is called the 'Rim'.
brim
circumference
A straight line from the center of a circle to the outer edge is called a radius.
Definition of "rim": 'the outer edge, border, margin, or brink of something, especially of a circular object.' From Old Norse rimi , raised strip of land.Thus, the "rim" of The Canyon itself is its outer edge -- ie, where the canyon stops and the level area begins.