Final answer:
A concise single sentence that summarizes and previews what a speaker will say during a speech is called a thesis statement.
Step-by-step explanation:
A concise single sentence that summarizes and previews what a speaker will say during a speech is called a thesis statement. This statement is typically found at the end of the introduction and provides an overview of the main theme or claim of the speech. It briefly touches on the key points that will be discussed in the body of the speech.