The ornamental design for a lamp, as shown and described.
FIG. 1 is a front perspective view of a lamp showing my new design.
FIG. 2 is a front elevation view of FIG. 1.
FIG. 3 is a rear elevation view of FIG. 1.
FIG. 4 is a right side elevation view of FIG. 1.
FIG. 5 is a left side elevation view of FIG. 1.
FIG. 6 is a top plan view of FIG. 1; and,
FIG. 7 is a bottom plan view of FIG. 1.
The surfaces are lightly lined for contour and no claim is made to any particular surface texture. The dashed lines indicated disclaimed portions of the design, and no claim is made to the designated portions indicated by dashed lines; including without limitation any power cord, lamp element, support feet, on/off switch, and on/off switch support plate, metal joining seam lines, joining plates and screws, bolt member or the upper head surface and bottom head surface portions as shown.