The number three; three things together; a ternary or triplet.
A section of paper for a book containing three double leaves or twelve pages.
Anything folded into thirds to resemble a trifold.
Any sheet of paper or cardboard, folded into three sections along two parallel creases and used to present information, typically as a brochure or display board.
A wallet with three equal-sized sections that fold together.
threefold
Of a mirror: having three reflective surfaces hinged together.