What is indicated by the term "superciliary line"?

The term "superciliary line" refers specifically to a marking that resembles an extended "eyebrow" line, typically located above the eye of a bird. This feature is particularly significant in avian identification, as it can vary greatly among species, helping birdwatchers and ornithologists differentiate between them. The presence or absence of such markings, as well as their color and prominence, can be a crucial aspect of describing and identifying a bird.

In contrast, the other options do not accurately reflect the meaning of "superciliary line." A marking on the wings relates specifically to wing patterns, which is separate from the facial marking indicated by the term. A type of feather does not correspond with the definition, and a white line on the torso represents a different region of the bird's anatomy altogether. Thus, the correct interpretation of "superciliary line" ties directly to the characteristic eyebrow-like marking around the eye area.