The ornamental design for a lamp, as shown and described.
FIG. 1 is a left perspective view of a lamp showing our new design;
FIG. 2 is a front elevation view of the lamp;
FIG. 3 is a rear elevation view of the lamp;
FIG. 4 is a right-side elevation view of the lamp;
FIG. 5 is a left-side elevation view of the lamp;
FIG. 6 is a top plan view of the lamp; and,
FIG. 7 is a bottom plan view of the lamp.
The portions of the lamp shown in broken lines form no part of the claimed design. The lamp is shown with symbolic breaks in its length, as appropriate. The appearance of any portion of the article between the break lines form no part of the claimed design.