In army fortification, a trench or ditch covered with a parapet providing you with communication between two trenches, specially the back and forward lines. Boyaus had been usually built in a zigzag pattern to stop experience of direct enemy fire from front.
A line, attracted winding about, to be able to enclose a few tracts of land, or even to attack some works.
A winding or zigzag trench creating a path or communication from 1 siegework to a different, to a magazine, etc.
In fort, a ditch covered with a parapet, serving as a way of communication between two trenches, especially involving the very first and 3rd parallels. Also referred to as a zigzag or a strategy.