We claim the ornamental design for a headphone, as shown and described.
FIG. 1 is a top perspective view of a headphone showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a sectional view taken in the direction of line 8-8 in FIG. 5, viewed along the headphone length with the internal parts being omitted.
The broken line showing of headphone is included for the purpose of illustrating environment and forms no part of the claimed design. Additionally, the unevenly broken lines in the drawings define the boundaries of the claimed design.