What is the difference between subvolcanic rocks and plutonic rocks?
Main difference between a subvolcanic verses a  plutonic is depth at which the rock solidified at from its molten state.  Plutonic implies a depth greater than subvolcanic by definition but I am sure there is some overlap between shallow end of plutonic and subvolcanic.  Depth of emplacement for plutonic would mostly be much greater than 2 km.

Plutonic is an igneous rock formed by solidification at considerable depth beneath the earth's surface. 

Subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at medium to shallow depths (&lt;2 km) within the crust.