The ornamental design for a lamp, as shown and described.
FIG. 1 is a perspective view of the lamp in a first configuration, illustrating my new design;
FIG. 2 is a front elevational view of the lamp;
FIG. 3 is a rear elevational view of the lamp;
FIG. 4 is an elevational view of one side of the lamp;
FIG. 5 is an elevational view of the other side of the lamp;
FIG. 6 is a top plan view of the lamp;
FIG. 7 is a bottom plan view of the lamp; and,
FIG. 8 is a perspective view of the lamp in a second configuration.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design, while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.