A Half Fold has two panels. Both panels are at full size.
A Tri-Fold has three panels. The two outside panels are at full size. The inside panel should be 1/16-inch narrower.
A Parallel Fold or Half-and-Half Fold has four panels. The two outside panels are at full size. The two inside panels should be 1/16-inch narrower.
A Z-Fold, also known as an Accordian Fold, has all panels at full size.