A heat source is a device or substance that generates thermal energy, which can be used to provide warmth or for other purposes such as cooking. This term usually refers to an external power supply that produces heat through various methods like combustion, electricity, or nuclear reactions. Some common examples of heat sources include stoves, heaters, and boilers. In the context of geology, a heat source is any natural process that generates thermal energy, such as volcanic activity or hydrothermal vents.