Some sheets of stamps have wide spaces or "gutters" which separate the sheet into four panes. A pair of attached stamps with a gutter separating them is known as a "gutter pair." The direction in which the gutter runs between the pair determines if it is a vertical or horizontal gutter pair. A block of stamps containing this gutter is called a "gutter block," and a block from the exact center of the sheet with two gutters crossing is known as a "crossed gutter block." | 
