Mountain fold
A mountain fold is a fold where the paper bends away from you, so the crease rises toward you like a ridge.
It is simply a valley fold made from the other side. You can fold the flap behind the model, or turn the paper over, make a valley fold, and turn it back. Diagrams show it as a dash-dot line, often with a hollow arrowhead pointing behind the paper.
Beginners often fold the flap toward themselves by habit, which gives a valley instead. Before creasing, check that the flap is disappearing behind the model. For small corner folds at the back, turning the paper over is usually more accurate.
