The ornamental design for a blade, as shown and described.
FIG. 1 is a top, front, right side perspective view of a blade showing my new design;
FIG. 2 is a front elevation view thereof, the rear elevation view being a mirror image of the front elevation view;
FIG. 3 is an enlarged right side elevation view thereof, the left side elevation view being a mirror image of the enlarged right side elevation view; and,
FIG. 4 is a top plan view thereof, the bottom plan view being a mirror image of the top plan view.
The broken lines in the drawings illustrate portions of the blade that form no part of the claimed design.