Speaking in Academic Contexts
Rhetorical Functions in Academic Speaking: Defining
In academic speaking, it is often necessary to define your terms.
The name we apply to the liquid rock material, or magma, when it reaches the surface, is lava. The word lava is also used for the solid rock that is formed by consolidation when the liquid rock cools. The temperature of lava as it comes to the surface may be higher than 2000°F. We know this because copper wire with a melting point of 2200°F was melted in the lava from Vesuvius. We have also observed a temperature of 2300° F at Kilauea.
Adapted from This earth of ours by Victor T Allen, p. 3
In this case, the term "lava" is being defined.
We call the sediment which is deposited by a stream alluvium.
This earth of ours by Victor T Allen, p. 97.
In this example, "alluvium" is being defined.
Diseases and symptoms
In this example, definitions of "disease", "symptom" and "sign" are defined.
X is ...
X is called ...
X is known as ...
X may be defined as ...
X is a type of Y that/which ...
A type of Y which ... is X
We call ... ...
We define ... ...