The ornamental design for a lamp, as shown and described.
1. Lamp
1.1: Perspective
1.2: Front
1.3: Rear view
1.4: Bottom
1.5: Top
1.6: Right side view
1.7: Left side view
Lamp in the shape of a squirrel, preferably for outdoor use; the lamp is provided with two light sources, respectively located inside the base and inside the nut; the nut is detachable to be used independently.