A closed (solid) dot means the endpoint is included in the curve and an open dot means it isn't. It's like the difference between "less than or equal to" and "less than". If the inequality is "strict" ( < or > ), we use an open dot to indicate that the endpoint of the ray is not part of the solution. For the other types of inequalities ( ≤ and ≥ ), we use a closed dot to indicate that the endpoint is part of the solution.
