Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

I often hear US citizens say something like this: <Some phrases>. Period. What does period mean when it appears in a sentence by itself in this type of situation?.
Period at the end of the sentence means, the things said in the sentence are definite and no change is allowed. For example, 'I want the document without any errors, period' meaning that there should not be any errors in the document.