border,
edge a strip forming the outer edge of something; "the rug had a wide blue border"
end (American football) a position on the line of scrimmage; "no one wanted to play end"
demarcation line,
demarcation,
limit the greatest possible degree of something; "what he did was beyond the bounds of acceptable behavior"; "to the limit of his ability"
surface the outer boundary of an artifact or a material layer constituting or resembling such a boundary; "there is a special cleaner for these surfaces"; "the cloth had a pattern of red dots on a white surface"