What does the slope of an force vs. displacement time represent?

I know that the area under the graph represents work, but what does the slope represent?

The spring constant is $k = \frac{F}{\Delta x}$
F is force applied to stretch a spring and causes it to extend by a length $\Delta x$ from its neutral position. If the neutral position is 0, then the displacement $\Delta x = x - 0 = x$
Let's say $k = 50 \frac{N}{m}$. It means that 50 N is required for every meter being stretched. If you graph $F$ v $\Delta x$, you get the slope $k$. Therefore the slope of the spring force F vs. x is the spring constant.