The ornamental design for a pillow, as shown and described.
FIG. 1 is a front perspective view of a pillow showing my new design;
FIG. 2 is a left side perspective view of the pillow of FIG. 1, the right side view being a mirror image thereof;
FIG. 3 is a top perspective view of the pillow of FIG. 1;
FIG. 4 is a bottom perspective view of the pillow of FIG. 1;
FIG. 5 is a rear, bottom perspective view of the pillow of FIG. 1;
FIG. 6 is a left side perspective view of the pillow of FIG. 1 rotated clockwise relative to FIG. 2, the right side perspective view being a mirror image thereof;
FIG. 7 is a top, front perspective view of the pillow of FIG. 1; and,
FIG. 8 is a left, rear perspective view of the pillow of FIG. 1, the right rear perspective view being a mirror image thereof.
The broken lines showing portions of the design in all figures is included for the purpose of illustrating environment and unclaimed features and forms not part of the claimed design.