The ornamental design for a pillow, as shown and described.
FIG. 1 is a first environmental perspective view of a pillow showing my new design being enjoyed by a user;
FIG. 2 is a second environmental perspective view thereof;
FIG. 3 is a front side view thereof shown in a first configuration;
FIG. 4 is a rear side view thereof shown in the first configuration;
FIG. 5 is a first side view thereof shown in the first configuration;
FIG. 6 is a second side view thereof shown in the first configuration;
FIG. 7 is a bottom view thereof shown in the first configuration;
FIG. 8 is a top view thereof shown in the first configuration; and,
FIG. 9 is an alternative top view thereof shown in a second configuration wherein peripheral portions of the pillow are spread to show an inner portion of the pillow.
The design details shown in broken lines form no part of the claimed design and/or are used to depict environmental subject matter that forms no part of the claimed design.