Boundary (noun)

1. A line that marks the limits of an area; a dividing line.
2. A real or imaginary line that separates different regions or domains.
3. A limit or restraint.

Origin:

Middle english boundarie, from anglo-french, from medieval latin boundarius, alteration of latin terminus limit, boundary.

Examples:

1. The boundary of the property is marked by a fence.
2. The boundary between the two countries is the river.
3. The company"s new policy is a boundary to the employees" freedom.
4. The athletes had to stay within the boundaries of the field.
5. The boundary of the city was expanding rapidly.