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This tag is referring to the process of identifying and closing questions that are duplicates of another question.

is referring to the process of identifying and closing questions that are duplicates of another question.

See comprehensive guidance here:

we want to tell the user ...something like, “Somebody already asked this. If that other question doesn't solve your problem, please clarify your question to explain how it's different.” Perfect: if the other question helps them, they're happy because they got an answer. If the other question doesn't help them, they know exactly what to do. No argument about how exact an "exact duplicate" needs to be...

Related articles at Stack Exchange blog

Dr. Strangedupe: Or, How I Learned to Stop Worrying And Love Duplication

...duplication is not necessarily bad. Quite the contrary — some duplication is desirable. There’s often benefit to having multiple subtle variants of a question around, as people tend to ask and search using completely different words, and the better our coverage, the better odds people can find the answer they’re looking for...

...use your good judgment and please continue to close and merge duplicates as you see fit. However, bear in mind that cultivating and supporting a moderate amount of natural duplication actively helps the community...

Handling Duplicate Questions

...there are three classes of duplicate questions, from most clear to least clear.

  1. Cut-and-paste duplicate questions. These questions are the very definition of exact duplicates; they are typically from users who willfully take the very same question and post it again... No grey area here.
  2. Accidental duplicates. These questions aren’t copy and paste, but they cover the exact same ground as an earlier Stack Overflow question. The overlap is not ambiguous...
  3. Borderline duplicates. These questions are ambiguous; they’re in the same ballpark as a previous question, but have subtle differences that may make them legitimately standalone questions. These are subject to interpretation...
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