The ornamental design for a mop head, as shown and described.
FIG. 1 is a perspective view of a sponge mop head showing my new design;
FIG. 2 is front view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a right side view thereof, the left side view being a mirror image thereof;
FIG. 5 is a rear view thereof; and,
FIG. 6 is a bottom view thereof.
The broken line showing of the portion of the mop handle, rectangular openings along the upper surface of the mop head, sponge, tabs on the under side of the handle and channels on the squeeze plate mechanism are for illustrative purposes only and form no part of the claimed design.