negative [photography]

Here is an article from Wikipedia on Gelatin silver print:
Before a paper is exposed, the image layer is a clear gelatin matrix holding the light-sensitive silver halides. For gelatin silver prints, these silver halides are typically combinations of silver bromide and silver chloride. Exposure to a negative is typically done with an enlarger, although contact printing was also popular, particularly among amateurs in the early twentieth century and among users of large format cameras.
I know what 'negative' means in general, but what does it mean here?

Hello stuartfang. The negative that you're looking for is in the WF dictionary, noun sense 2: a negative photographic image from which positive prints may be made.

More explicitly (for those of you of the digital generation) photographs were created prior to digital by using film. Once the film was exposed it would be developed which made it no longer light sensitive and would yield a "negative". In black and white, the image would appear in opposite tonal value to what would appear on the print. Hence, the term "negative". That is, what is going to print as white would appear as black on the negative. The negative was transparent except for the areas that had been exposed, which would in varying degrees be rendered grey or black.

So the term "negative" came from the original black and white film of yore. The term stuck with color, but the colors of the color negative do not appear to be "negative" to the human eye.