Most phrases can be understood by thinking about what each word means.
General meaning
Back means rear, or farthest away
Boundary means a specified line separating two places.
A line is often thought of as straight, but can be an uneven line. A line also delineates areas.
So a "back boundary line" is a specified boundary at the rear.
Your back yard has a "back property line" as does a tennis court.
Note: Also see Tennis terms.
the back boundary line, and the long service line
The back of a badminton court is a back boundary line and long service line for singles.
The boundary line is solid. If not it will be a dashed line.
The official definition of boundary is "a line that marks the limits of an area; a dividing line."
A boundary is a restriction, a line of demarkation. That fence is the boundary between our property. The ball went outside of the boundary.
The boundary line under the basket is known as the baseline.
A boundary is a dividing line that separates one area from another.
The boundary of the set of rational numbers as a subset of the real line is the real line.
The Boundary Line - 1915 was released on: USA: 20 February 1915
The cast of The Boundary Line - 1925 includes: Fred Humes
It's the line (boundary) between two countries.
the treaty line