Rusty Hi Rusty, Extrusive means the material makes it to the surface. Intrusive means that it doesn't make it to the surface and therefore cools and solidifies below ground. Another synonym of extrusive is volcanic, where as the synonym for intrusive is plutonic. Of course, within a volcano, the magma has to intrude through the body of the volcan before it erupts. Sometimes this magma doesn't make it and forms an intrusion.
Most volcanoes therefore have both types of activity going on.