In philately, tête-bêche (French for “head-to-tail”, lit. “head-to-head”) is a joined pair of stamps in which one is upside-down in relation to the other, produced intentionally or accidentally. Like any pair of stamps, a pair of tête-bêches can be a vertical or a horizontal pair. In the case of a pair of triangular stamps, they cannot help but be linked “head-to-tail”.
A gutter is the space left between postage stamps which allows them to be separated or perforated. When stamps are printed on large sheets of paper that will be guillotined into smaller sheets along the gutter it will not exist on the finished sheet of stamps. Some sheets are specifically designed where two panes of stamps are separated by a gutter still in the finished sheet and gutters may, or may not, have some printing in the gutter. Since perforation of a particular width of stamps is normal, the gutter between the stamps is often the same size as the postage stamp.
* Text from Wikipedia