Tectonic plates are parts (pieces) of the outermost layer of Earth: the Crust. (the outermost part of the mantle is also often included in the plates). This means that the land in the middle of the plates is relatively stable while the borders of the plates can be in movement - after all this is where two pieces meet. Plate borders are where the vocanoes and Earthquakes often take place.
Can you give a closer picture?
