Intrusive Rocks

Igneous rocks which form by the crystallization of magma at a depth within the Earth are called intrusive rocks. Intrusive rocks are characterized by large crystal sizes, i.e., their visual appearance shows individual crystals interlocked together to form the rock mass. The cooling of magma deep in the Earth is typically much slower than the cooling process at the surface, so larger crystals can grow. Rocks with visible crystals of roughly the same size are said to have a phaneritic texture.

A body of intrusive igneous rock that crystallizes from cooling magmas beneath the Earth's surface is called a "pluton". If the pluton is large, it may be called a batholith or a stock. Minor plutons include dikes and sills. If a penetrating intrusion cuts across the geological layers it is called a dike. If it runs parallel to the layers, it is called a sill. If an intrusion causes the rocks above to rise and form a dome, it is called a laccolith.

References: geocases.uk.
Wiki:dike

Extrusive Rocks

Igneous rocks which form by the crystallization of magma at the surface of the Earth are called extrusive rocks. They are characterized by fine-grained textures because their rapid cooling at or near the surface did not provide enough time for large crystals to grow. Rocks with this fine-grained texture are called aphanitic rocks. The most common extrusive rock is basalt.