When stamps are produced at printer shops, they come off the press in large sheets (Uncut Press Sheets). Each sheet contains a set number of panes, and each pane contains a set number of individual stamps. Think of a sheet of stamps as you would a large window. Panes of stamps on a sheet are just like windowpanes. The most common configuration of panes on a sheet is 6, but there can be 4, 5, 8, 9, 10, or 12 panes per sheet as well. (Nine is the 2nd most common.)
Plate position refers to the place on the sheet where an individual pane is located. Plate position, therefore, means pane position. Many philatelists like to request a specific plate position, when they purchase stamps. This keeps their collections consistent. If, for example, you wants an Upper Right position, your stamps will come from the pane located in the upper right corner of the sheet. This is easy to visualize when a full pane of stamps is purchased. However, there are instances when stamps can be purchased in smaller formats (blocks or strips) with a plate position, provided the value of the stamps allows this choice. These cases are a bit trickier to picture, so it’s important to remember that the plate position still refers to the position of the pane on the sheet, not the position of the block or strip on the pane.
Each plate position has its own suffix code. The most commonly requested positions are Upper Right (suffix code #1), Upper Left (#2), Lower Right (#3), and Lower Left (#4). An easy way to remember these suffixes is to think of a backward letter ‘z’.