ACOG: Advanced Combat Optical GunsightAO: Adjustable Objective. Parallax correcting feature located at the end of the scope (objective lens).
BDC: Bullet Drop Compensation. A BDC scope compensates for the possible effects of gravity, wind conditions, etc, on the bullet’s trajectory.
Clicks: Number of times you will turn the turret when fine-tuning while zeroing your scope.
Elevation: Vertical crosshair of the optic.
Eye Relief: How far your eye should be from the rear lens (eyepiece) so the image is clear.
Eyepiece Lens: This is the lens that is closest to your eye. It is also referred to as an Ocular Lens.
FFP: First focal plane. The crosshairs in FFP scopes increase in size as magnification increases.
Field of View: Area that you can see through the scope at different magnification levels.
IR: Illuminated Reticle. These reticles light up when turned on. It makes it easier to see if there is not enough ambient light.
LPVO: Low Power Variable Optic. A scope where the magnification begins at 1x.
LR: Long Range.
MIL: Millradians of Angle. It is used to determine the elevation and windage adjustments. This measurement system is more often found in European optics.
MOA: Minute of Angle. It is used to determine the elevation and windage adjustments. This measurement system is more often found in American optics.
Ocular Lens: This is the lens that is closest to your eye. It is also referred to as an Eyepiece Lens.
Objective Lens: This is the end of the scope that is flared.
Parallax: These adjustments allow you to clearly view the crosshairs and the target simultaneously. Without parallax adjustment, it is difficult to have a close object and a faraway object in focus simultaneously. This is mainly needed at higher magnifications.
Picatinny: A rail system for mounting a scope to a rifle.
POI: Point of Impact. This refers to your target or where you intend for the bullet to hit.
Power: Magnification of the scope. If a scope is listed as 3-12x42mm, the magnification is 3x – 12x.
Reticle: The crosshairs of the scope.
Rimfire: Where the firing pin strikes the bullet.
RS: Rifle Scope.
RTA: Rapid Target Acquisition
SFP: Second Focal Plane. With an SFP scope, the crosshairs remain the same size as magnification increases.
SS: Sun Shade. It attaches to the rifle scope to provide shade from the sun when shooting.
Subtension: Area of the target that is within the crosshair.
Turrets: These are the knobs or dials on the scope that allow for adjustments in elevation and windage.
Variable Power: The range of magnification for a scope. For a 3-12x42mm, the range of magnification is 3x – 12x.
Weaver: Type of mount for a rifle scope.
Windage: Horizontal crosshair of the optic.