I am trying to understand the concept of natural language processing. Can you provide a brief explanation of what it is and its main applications? Please ensure your response contains at least 2 placeholders represented by square brackets, such as [application_1] and [application_2]. Additionally, your answer should be structured into 2 sections, with each section starting with "Section 1" and "Section 2" respectively. Finally, include a postscript starting with "P.S." at the end of your response.
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