I claim the ornamental design for a pillow, as shown and described.
FIG. 1 is a perspective view of a pillow, showing my new design;
FIG. 2 is a front elevational view thereof, the rear elevational view being a mirror image thereof;
FIG. 3 is a left-side elevational view thereof, the right-side elevational view being a mirror image thereof;
FIG. 4 is a top plan view thereof; and,
FIG. 5 is a bottom plan view thereof.
The broken lines showing reading material and glasses in FIG. 1 and the fasteners in FIG. 5 depict environmental matter and form no part of the claimed design. The remaining broken lines represent stitching, and are part of the claimed design.