The correct distinguishing feature from the options provided is:
A postulate is assumed to be true, and it does not have to be proven.
To clarify the other options:
- A conjecture is a statement that is believed to be true based on observations but has not yet been proven.
- A theorem is a statement that has been proven to be true through rigorous logical reasoning based on previously established statements such as postulates and other theorems.
- A definition explains the meaning of a term or a concept and does not necessarily involve proof or observation.
So, the only accurate statement in your options is that a postulate is assumed to be true and does not require proof.