A tri-fold brochure is formed from one sheet, in most cases A4 paper size is used and it is folded twice (in different lines between them, vertical and parallel) to form three pages, this is why it is called tri-fold format.
These three pages have two sides, which mean that the total pages that are available are six.
You must remember that the content of the tri-fold brochure must be adapted to four pages, as the front page of the brochure will be used for the title/catcher of attention and the back page usually contains the contact information.
Tri-fold brochures generate curiosity on the reader, as it requires them to open it up. They are easy to carry, as they have a convenient size. They are fast to create and fairly economic to print.