I am assuming that you are talking about hotspots in regard to Earth science and plate tectonics. A hotspot is best described as a weakened section of the Earth's mantle that allows liquid magma to emerge from the mantle at a particular point on the Earth's surface. As the magma comes into contact with the crustal plate sitting above it, the plate itself weakens and allows the magma to rise to the surface as volcanic lava. If the hotspot is located under the ocean, a volcanic island will form. As the plate moves across the surface, the location of the hotspot shifts with regard to its location in relation to other land masses. A perfect example of this are the Hawaiian Islands. They were formed as the Pacific plate moved from east to west and deposited lava which became the islands.