LBF means Ledged, Braced and Framed, to give the door strength and rigidity.
This picture shows a door made of boards. The horizontal pieces are called ledges. You'll need as a minimum one at the top and one at the bottom. The middle one improves it and you can put a lock there.
The diagonals are called Braces, to prevent the door sagging and to carry the weight to the hinges. As your door is faced with ply these are less important.
A Frame is reinforcement going all round the sides top and bottom, which greatly improves strength and rigidity and allows you to fit hinges, bolts and locks.
The cut edges of ply allow water to penetrate which will quickly degrade it and it will fall apart. Lipping on a door is strip of wood fixed to the edges to protect and seal them
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Here's one,
View attachment 308417