Using “a fraction” to mean “a small amount” is a pet peeve of mine. I have a math background, therefore to me a fraction is “any numerical quantity that is not a whole number.”
Thus, in a forest of 10,000 trees, if you cut down one tree, the remaining forest is a fraction of its original size (9999/10000 is a fraction).
I know that “fraction” in general use actually means “a small amount.” Like I said, it’s just a pet peeve of mine. :p