Autofocus: This score depends on the autofocus speed of the lens, the ability to override the focus with a turn of the focus collar, etc.
Bokeh: Should have a creamy quality, have highlights that are natural shapes, etc. Longitudinal chromatic aberration (LoCA), if present, also negatively affects this score.
Color Fringing: This score is affected by both the chromatic aberration and LoCA of the lens.
Contrast: the ability of the lens to resolve detail — related to the sharpness of the lens.
Distortion: This score has to do with the ability of the lens to keep straight lines straight.
Flaring: This score has to do with the ability of the lens to control light reflections between its elements, control flaring, control ghosting, etc.
Infrared: The ability of the lens to take in infrared light without creating a hot-spot in the center of the image. Because not all lenses have infrared scores, this is always ignored in the overall score of a lens.
Manual Focus: This score has to do with the experience of manually focusing the lens — the width of the focus collar, the focus throw angle, the resistance of the grease on the helicoil, etc.
Maximum Aperture: Lenses are given a score based on their smallest maximum aperture, so variable aperture lenses are always rated based on their smallest wide-open aperture.
Mechanics: This score has to do with the the quality of the lens assembly, zoom creep (when applicable), the ability of the lens to keep dust out, etc.
Sharpness: the ability of the lens to resolve detail — related to the contrast of the lens.
Vignetting: This score has to do with the ability of the lens to limit darkness in the corners and borders of the image.