Reticle

The reticle is what the rest of the world calls "crosshairs." In the distant past, these were actual threads of silk or spider webs, but today they are more often either thin metal wires or even lines etched on glass. Reticles are housed in a tube called the erector tube and the adjustment knobs move this tube in the desired direction. That's why the reticle lines appear centered on nearly all scopes. A few scopes from Europe have reticles that actually move in your field of view when they are adjusted, but most shooters prefer reticles that are always centered.