The ornamental design for a desk, as shown and described.
FIG. 1 is a perspective view of a desk showing my new design;
FIG. 2 is a front view thereof, the rear view being identical thereto;
FIG. 3 is a right side view thereof, the left side view being identical thereto;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is an enlarged detail view indicated by line 6-6 in FIG. 2;
FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 6;
FIG. 8 is another perspective view thereof shown in use;
FIG. 9 is another perspective view thereof shown in use; and,
FIG. 10 is another top view thereof shown in use.
The broken line subject matters in FIGs. 8-10 are included for the purpose of illustrating unclaimed environment and form no part of the claimed design.