Since the graph is not provided and you have not describe which temperature is represented by x or y, we cannot tell what the meaning of any particular coordinate might be. In general, the meaning is the temperature value on the vertical scale that corresponds to zero on the horizontal scale.
For example, if the horizontal (x) scale is °C, then the y-intercept will be 32 °F, the value on that scale that corresponds to 0 °C.
If the horizontal scale is °F, then the y-intercept will be -17 7/9 °C, the value on that scale that corresponds to 0 °F.
