Any paper or board weight over 200gsm requires a crease to enable folding without cracking on the material (through the printed image)
Bruising or indenting a line in paper, cardboard, etc., to facilitate folding.
When folding it is often necessary to pre-crease. Best results are obtained when folds are made parallel to the grain. Always fold into the bead. Creasing on a litho machine or with the Rotary score method will not always give a satisfactory result.