I claim the ornamental design for a backpack, as shown and described.
The patent or application file contains at least one drawing executed in color. Copies of this patent with color drawing(s) will he provided by the Office upon request and payment of the necessary fee.
FIG. 1 is a front perspective view of a backpack according to the present invention from the right side thereof. The left side of the backpack is a mirror image of the right side; and,
FIG. 2 is a rear view of the backpack of FIG. 1.
The bottom of the backpack is unornamented and forms no part of the claimed design. The grayed out portions of the backpack form no part of the claimed design. The dash dot dash line depicts the claim boundary and forms no part thereof.