Zero
The distance at which your scope's reticle and the bullet's flight path coincide. "100-yard zero" means the bullet hits exactly where the crosshair is at 100.
Choose a zero distance and confirm it. Most precision shooters use a 100-yard zero because dope (drop and wind) past that is well documented and easy to dial.
A 100-yard zero means the bullet is climbing for the first stretch (the scope sits above the bore) and then falling. The bullet crosses line-of-sight twice, once near the muzzle, once at the zero.