I hear "Tone", "Tonal scale/range" in the context of photography. What does it actually mean?
It can mean one of two things in colour photography:
the overall lightness or darkness of an area of an image, similar in meaning to "luminosity"; or
the colour of all or part of the image, usually in relation to its warmth (bias towards red, orange and yellow) or coolness (bias towards blue and green).
In black and white photography, the luminosity meaning is the same, but the colour aspect refers to the colour of the paper and the developed image, with "warm tone" prints generally tending towards brown or sepia on a natural fibre base and "cold tone" prints tending towards blue or purple on an artificially whitened ground.
When people talk about a "tonal range", they are talking about the difference between the lightest and darkest areas of the picture. It can refer to either the overall contrast of the image or to the local contrast in parts of the image (with the overall contrast moderated by burning and dodging). A "tone scale", on the other hand, usually refers to an external reference image divided into distinctly different regions of lightness or darkness, like Ansel Adams' Zones 0-X.
In photography tone is the range of lightest to darkest part of an image. Human eye can distinguish brightness range from details in the lightest areas to darkest with ratio 1:1,000,000. Film or digital image sensor have tonality range of 1:200. It’s 5,000 times less sensitive than our eye.