The ornamental design for a pillow, as shown and described.
FIG. 1 is a front, top, and right-side perspective view of a pillow;
FIG. 2 is a front-elevational view thereof;
FIG. 3 is a rear-elevational view thereof;
FIG. 4 is a right-side elevational view thereof;
FIG. 5 is a left-side elevational view thereof;
FIG. 6 is a top-plan view thereof; and,
FIG. 7 is a bottom-plan view thereof.
The evenly spaced broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design. The dot-dashed broken lines represent the unclaimed boundaries of the design. In addition, the surface shading illustrated in the drawings is provided merely to highlight the contour of the design; it is not intended to be illustrative of texture or gloss.