The tag [tag:etcs] has now 7 occurrences *[edit: **had** 7 occurrences]*. 

It stands for "elementary theory of the category of sets". I suggest to manually change it to [tag:elementary-theory-category-sets]. (This is 31 letters. [tag:elementary-theory-category-of-sets] would be 34 letters, is maybe suitable too.)

I believe abbreviations should be avoided in tags (exceptions only being very famous ones such as PDE, ODE).

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Edit: now changed to [tag:elementary-theory-category-of-sets].