The reticle is a piece of polar glass with a surface, line, circle or other graphic that helps define the aiming point in the field of view, typically mounted on the telescope's right eyepiece focal plane.  According to the graphic distribution on the reticle, it can be divided into: Crosshair Reticle, Dot Reticle, German X Reticle, Duplex Reticle, BDC Reticle, Mil Dot Reticle and Christmas Tree Reticle.