A transform Boundry. It is the moving, banging, crunching, grinding, and occasional snagging or binding up of these plates which causes earthquakes and volcanic eruptions. It is no surprise then that more earthquakes and volcanoes occur in the Pacific Ocean regions where there are more convergent and transform fault plate boundaries. In contrast, the Atlantic Ocean region is fairly calm by comparison since its plates tend to diverge, creating new crust. One additional element of plate tectonics is hot spots.
Some volcanoes occur within a plate and are called intra-plate volcanoes.
It is apparent that planet Earth is a dynamic system which needs to continuously release internal heat. Plate tectonics has provided a reliable theory to explain the interactions which occur between the inside and outside of Earth's surface. The following diagrams depict the major tectonic plates of the world and the continents which ride on them. As you look at these plate boundaries, notice the jagged edges which define the plate boundaries. Notice also which plates are the largest and which are the smallest.