A more thorough explanation:

Arcifinious (ahr-sə-fin-ee-əs), adj. [from Latin arcifinius “having irregular boundaries”] is a term used in civil law to describe:

1. A landed estate that has natural boundaries such as woods, mountains, or rivers.
2. A country that has a frontier that forms a natural defense.

1. The estate was arcifinious, with the river forming its natural boundary.

2. Switzerland is an arcifinious country, with the Alps forming a natural defense against invaders.

These examples illustrate how arcifinious is used to describe a property or country that has natural boundaries that define its limits or provide a natural defense. In the first example, the river serves as a natural boundary for the estate, while in the second example, the Alps provide a natural defense for Switzerland.