Have you heard of Gurupurnima?

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Recently got to know about a festival named Gurupurnima. As the name suggests, I guess it must be something like Teachers Day. What is this festival all about. What is it celebrated for. In whose memory is this celebrated. Who was the main Guru in whose honour it is being celebrated every year. When and how is it celebrated. Is it just another name for Teachers Day or one of its own. Since when is this being celebrated? People of which place and caste celebrate it? I think I have a lot more questions about this festival recently heard of, by me. I hope somebody throws light on this festival for me.