The equation, "Thing X is Thing Y," describes: 3. Metaphor.
Metaphor is a figurative language that compares things directly by stating that one thing is another. Unlike simile which is also a form of comparison, there is no usage of like or as.
So when we say that Thing X is Thing Y we are using metaphor.
Learn more about metaphor here:
https://brainly.com/question/9418370