1. Soliloquy: A soliloquy is a speech delivered by a character in a play or literary work when they are alone on stage, and it is a form of monologue where the character expresses their inner thoughts and feelings. It is not a speech without preparation.

2. Rhetoric: Rhetoric refers to the art of effective or persuasive speaking or writing. It involves using various techniques and strategies to make a speech more convincing and impactful. It does not specifically refer to a speech delivered without previous preparation.

3. Extempore: An extempore speech is a speech delivered without prior preparation or rehearsal. It is often done spontaneously, in response to a prompt or question. This is the correct term for a speech that is not planned in advance.

4. Expression: "Expression" is a more general term that can refer to various forms of communication, including speech, but it does not specifically describe a speech delivered without preparation.

Therefore, the term "extempore" best fits the description of a speech delivered without previous preparation, making option (3) the correct choice.