What does defined boundary mean

Something that indicates or fixes a limit or extent. Those two trees mark the boundary of our property. The mountain range that forms the country's northern boundary.

Explanation:

It is one of these meanings because I don't know what type of boundary you mean.

Defined boundary is a fixed line (which can be imaginary or not) that marks a boundary.

Explanation:

Defined boundary is a fixed line (which can be imaginary or not) that marks a boundary. Through it it is possible to make more than one division between regions, because it can be used to determine the real limits of a country, or any type of territory in a physical and efficient way.

These limits can be established through walls, fences, or even political, cultural and religious ideologies. The important thing is to separate two regions that cannot be understood as one, due to several different factors.