The ornamental design for a backpack, as shown and described.
FIG. 1 is a front view of a backpack of the present invention when the top of the backpack is in a closed configuration.
FIG. 2 is a rear view thereof, partially exposing the pockets on the rear side of the backpack.
FIG. 3 is a left view thereof.
FIG. 4 is a right view thereof.
FIG. 5 is a top view thereof.
FIG. 6 is a bottom view thereof.
FIG. 7 is a first perspective view thereof.
FIG. 8 is a second perspective view thereof.
FIG. 9 is a rear view of the backpack of the present invention when the two straps in the backside of the backpack are separated wide, exposing more fully the pockets on the rear side of the backpack.
FIG. 10 is a top view of the backpack of the present invention when the top of the backpack is in an open configuration, showing two interior side shoe compartments; and,
FIG. 11 is a perspective view of the backpack of the present invention when the top of the backpack is in an open configuration, showing the two interior side shoe compartments.
The broken line showing of certain portions of the backpack is included for the purpose of illustration only and forms no part of the claimed design.