That is called symbolism, where a specific object, person, or event is used to represent a deeper meaning or idea.
symbolism
Bunny pegs.
The words 'substitute' and 'proxy' both mean using one thing to stand for another.
Kick stand?
To use one thing to stand for another.
When you say one thing is another, it is called a metaphor.
That thing is called mistletoe.
The thing you stand behind when giving a speech is called a podium or a lectern.
It is called an analogy
A living thing that produces another living thing like itself is called a parent.
Example synonyms for something used in place of another thing are: substitute surrogate proxy stand-in replacement representative
When thermal energy moves from one thing to another it is called heat energy.