The immune system is a complicated and intricate system that contains specialized cells and tissues that protect us from external invaders and our own altered cells. Which term is used to define any substances capable of inducing a specific immune response and of reacting with the products of that response?

An Antigen.

Any substance that triggers an immune response is known as an Antigen.

Explanation:

An Antigen is a substance usually protein that triggers or stimulates the body to produce antibodies.

These antibodies produced by the body helps the body to fight off virus,fungi and  bacteria and other harmful thing that invades the body to harm it.

Antigens are foreign to the body and therefore stimulates a response immediately the body notices it.

Antigens can also come inform of foreign bodies that trigger the body to produce antibodies for defence.

Explanation:

If youre here for study island, the answer is "an invasion of a microorganism from the external environment"

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.