Slope

Here are two snapshots of Joan catching bugs:

Notice that when Joan caught the green fly, she had to stick her tongue almost straight up in the air. When Joan caught the yellow fly, her tongue was close to flat.

Lines can be slanted different ways, just like Joan's tongue:

We use slope to measure a line's slant. The green line above has a big slope, because it is slanted so sharply. Because the red line is close to flat, it has a small slope.

Lines with negative slope point down instead of up. Here is a line with a negative slope: