A loosely defined term with a number of current usages. Many petrologists use it to describe igneous rock bodies which have crystallized at great depth, there being no real agreement about what is meant by ‘great depth’. Other petrologists use the term to describe any igneous rock that forms in largish intrusions (i.e. excluding dykes and sills). ‘Plutonic’ has also been used to describe the origin of magmas and gas derived from near the base of the crust or in the upper mantle.