A sunspot is a (relatively) cool area on the Sun’s surface (photosphere) which has an enormous amount of magnetic activity. A sunspot is a temporary phenomena on the Sun’s photosphere.
The amount of sunspots visible at any time on the Sun changes periodically, as the Sun goes through a cycle of activity which lasts roughly 11 years.

The strong magnetic fields of sunspots are also responsible for solar flares, which in turn cause the Aurora Borealis (Northern and Southern Lights) here on Earth.