What does plutonic means in geology ?

Plutonic : definition

A plutonic rock is an igneous rock formed by the slow crystallization of magma at depth (a few hundred meters to several kilometres), usually characterized by a grainy texture. The most common of these rocks are granites (dominant), granodiorites, diorites and gabbros.

Depending on the composition, we distinguish acid plutonic rocks (rich in quartz, such as granites), intermediate (syenites), mafic (gabbros), ultrabasic (peridotites) or alkaline (rich in alkaline and poor in silica).