The ornamental design for a lamp, as shown and described.
FIG. 1 is a first perspective view of a lamp showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a back view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof;
FIG. 8 is a bottom view thereof; and,
FIG. 9 is an enlarged view of the selected portion in FIG. 1.
The broken lines shown in the drawings depict portions of the lamp in which the design is embodied that form no part of the claimed design. The additional dash-dot-dash lines surrounding the detail views in FIGS. 1 and 9 are for annotative purposes only and form no part thereof.