Hola Jessica!
Essentially it's a horizontal, dashed line crossing directly over the -4 in the y-axis.
Keep in mind stuff like y = h or y </>/≤/≥ h all result in horizontal lines with it crossing directly over h. x = v or x </>/≤/≥ v all result in vertical lines crossing directly over v.
< = dashed-line; shade above line
> = dashed-line; shade below line
≤ = solid-line; shade above line
≥ = solid-line; shade below line