what is an informal persuasive speech?
I would imagine that "informal" means casual, not like giving a lecture or a speech at an formally organized meeting. "Persuasive" indicates that you are trying to influence others to do something by what you are telling them.
I searched Google under the key words "informal persuasive speech" to get this possible source:
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Here are some other sources of information:
This may be more than you wanted, but I hope it helps. Thanks for asking.