The finished size of a printed document refers to its final dimensions, after it's been trimmed and folded to its final shape.
For example, if you wanted to create an A4 newsletter by folding an A3 sheet of paper in half, you would need to specify the finished size as A4 (210x297mm) and the folding as half-fold. This would result in a finished document featuring four A4 panels.
Similarly, if you wanted to create a DL-sized document by folding down an A4 sheet of paper, you would specify the finished size as DL (99x210mm) and the folding as C-fold. This would result in a finished document that is DL in size with six panels.
If in doubt, please contact us for further information. We're always happy to help.