These are short submissions that contain important new results and are intended for faster publication. Letters are given priority handling. While there is no page limit, typical letters are 3-4 printed pages and have fewer than five figures.
This is written in a scientific journal for the contributing authors. What does it mean exactly. While they say typically you adhere to those standards and can also include more than pages and figures, does the typical letter have maximum 4 or 5 figures? Scientific language is normally very accurate, so the phrasing 4 figures mathematically "less than 5" makes me unsure. In my mother language we would not phrase it like this.