Fill in the blank.The expression f(x + h) − f(x)h, h ≠ 0,

Question

is called the

Answer 1

The way you typed it, not much

if you meant
( f(x + h) − f(x) ) / h, h ≠ 0
then you have the slope between the points (x, f(x)) and (x+h, f(x+h))
sometimes called the difference quotient.

If you take the limit, that is,
limit (f(x + h) − f(x)) / h, h ≠ 0 then it is called the derivative, or the slope of the tangent to f(x) at the point (x, f(x) )