A heat lamp is a lamp (light) with the main purpose of making heat. This is commonly infrared light but white light incandescent lightbulbs are also used. Sometimes the glass of the light bulb is colored to cut out yellow and even higher frequency light (to let the infrared light through, which has most of the heat).
Humans can use these lamps to keep warm, to warm a part of the body that is injured and needs gentle heat, etc. These lamps are also frequently used to keep baby chickens, piglets or other baby animals warm.