The ornamental design for a lamp, as shown and described.
FIG. 1 is a top, front and left perspective view of my new design for a lamp showing a bulb holder in a first, wrapped, position;
FIG. 2 is a bottom, rear and right perspective view of the lamp; and,
FIG. 3 is a top, front and left perspective view of the lamp, the bottom and rear perspective view being identical to that of FIG. 2 with the exception of the position of the bulb holder which is in a second, unwrapped, position.
The speckled dots are intended to illustrate a contrast in color and/or contour of the claimed invention. The fact that the drawings illustrate dots, in and of itself, is not material or part of the invention.