Wiktionary
n. (context photography English) A lens which produces an image similar in detail and angular perspective to the view produced by the human eye, as distinct from a wide-angle lens or a telephoto lens.
Wikipedia
In photography and cinematography, a normal lens is a lens that reproduces a field of view that appears "natural" to a human observer.
However, to find a photographic lens equivalent to the human eye, which has an effective focal length of approximately 17mm, is problematic due to the nature of human binocular vision, being mediated and processed by the cortex, and because of the structure of the human eye which has a concave retina, rather than a flat sensor, with variable sensitivity and resolution across its wider-than-180° horizontal field-of-view.
A normal lens then, is one that renders a printed (or otherwise displayed) photograph of a scene that when held at 'normal' viewing distance (usually arms-length) in front of the original scene and viewed with one eye, matches the real-world and the rendered perspective.
Usage examples of "normal lens".
It was so vast that it looked like a telephoto lens shot, even through a normal lens, and when the cameramen enhanced it with their telephotos (as none of them could resist doing) it looked like a giant ice-covered asteroid looming over the shoulders of William A.
With 35mm a lens that size gives you about a twenty-power magnification, so at a hundred yards it would give the same as a normal lens fifteen feet from the subject.
Presumably the cameras would automatically convert to a normal lens when the indoor lights were on or during daylight.