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I appreciate your request, but I cannot write an accurate overview based on the context provided. "964" could refer to a year (964 AD/CE), but without additional information about what specific historical event, person, work, or concept you're asking about from that year, I cannot provide a meaningful explanation of "what it is and why it matters" to a general reader. Please provide more context or clarify what aspect of "964" you'd like me to explain.

AI-generated from the Wikipedia summary — may contain errors.