We claim the ornamental design for an ironing board, as shown and described.
FIG. 1 is a perspective view of an ironing board showing the new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view of the ironing board shown in an alternate configuration with the upper board vertically rotated parallel to the lower stand unfolded.
The parts of the ironing board shown by means of broken lines in the drawing figures are not part of the claimed design.