Aspheric lenses
Aspheric lenses, called such due to their surfaces being aspheric unlike regular lenses that have spherical surfaces (a cross-section of an aspheric lens woulde describe a curve similar to a very shallow bell-curve). Aspheric lens design corrects colour fringing, improves edge definition and reduces field curvature (barrel distortion).

BaK-4
High Index Barium Crown Glass. Highest quality prisms used in binoculars to collimate internal light and produce sharper, clearer images.

Fully coated
All glass-to-air surfaces (lenses or prisms) are coated several different substances such as magnesuim fluoride and to increase light transmission through the lens surface, and to decrease the amount of reflection that occurs. Lenses coated with regular anti-reflective coating create a slight purple or blue reflection off their surface.

Multi coated
Glass-to-air surfaces (lenses or prisms) are coated with up to seven different substances such as magnesuim fluoride and cerium oxide to increase light transmission through the lens surface, and to decrease the amount of reflection that occurs. Multi coated lenses transmit more light and decrease reflected light more efficiently than regular coating. Multi-coated lenses create a slight green reflection.

Porro prism
Two triangluar prisms are affixed to a shelf in the binocular barrel at right angles to each other causing the light path through the objective lens to be "folded" several times thus effectively increasing the length of the light path whilst keeping the binocular length relatively compact. Prism material can be BK7 (historically used only to make lenses prior to World War Two), or BaK4. This design results in a binocular with shoulders, having the eyepieces and objective lenses not coaxially aligned.

Roof prism
Two or more prisms are cemented together to form a single complex prism assembly. This design is more expensive to produce than porro-prisms because the tolerances required to produce a good image are much tighter. Images through roof-prims binoculars have a less pronounced 3D quality, but the binoculars tend to be more compact.

Wide Angle
If the angular field of view of a binocular is greater that the result given by dividing the binocular's magnification into 65, then that binocular is considered to be wide angle. Wide angle binoculars let the viewer see more side-to-side than regular binoculars. This can be of great benefit in many situations, and invaluable in others. Beneficial for bird-watching, game-watching and sport-watching, and most other use.