A thesis in a speech is the one main idea the speaker wants you to accept or remember, stated in a single sentence or, at most, a couple of sentences. It's the claim everything else supports.
Picture a town meeting: Our park needs lighting before dark evenings make it unusable. That's the thesis, and the rest of the talk backs it up.
Thesis in two speech examples
Imagine a school assembly. The speaker says, Volunteering an hour a week changes both the helper and the neighborhood. That one sentence is the thesis, and every story that follows exists to support it. Placed early and restated at the end, it is normal for a speech, though not a strict rule.
To decide whether a speech has a clear thesis, listeners can test it with one question: did the whole speech back a single claim? If the stories, reasons and figures all point back to that one idea, that idea is the thesis.