perimeter

Short definition from Wiktionary

Noun

1. 1
   The sum of the distance of all the lengths of the sides of an object.
2. 2
   The length of such a boundary.
3. 3
   The outer limits of an area.
4. 4
   A fortified strip or boundary usually protecting a military position.
5. 5
   An instrument for determining the extent and shape of the field of vision.