the border or outer boundary of a two-dimensional figure.

the length of such a boundary.

a line bounding or marking off an area.

the outermost limits.

Military . a fortified boundary that protects a troop position.

Ophthalmology . an instrument for determining the peripheral field of vision.

noun

center , inside , interior , middle

noun

ambit , borderline , boundary , bounds , brim , brink , circuit , compass , confines , edge , fringe , hem , limit , margin , outline , periphery , skirt , vergenotes:parameter is a quantity or mathematical variable that stays constant; perimeter is the outer boundary of an area , edging , rim , verge , border , circumference , edges