I have noticed that the tag [tag:duality] is quite often used for questions about dual spaces in [functional analysis](https://mathoverflow.net/questions/tagged/duality+fa.functional-analysis) and [linear algebra](https://mathoverflow.net/questions/tagged/duality+linear-algebra). However, it's not immediately clear from the tag name that this is intended. (Although the current revision of [the tag-excerpt](https://mathoverflow.net/posts/235818/revisions) explicitly mentions dual spaces.) 

In addition to that, duality is a word which is used in [several different - although related - meanings](https://en.wikipedia.org/wiki/Duality).

> I suggest to create a separate tag [tag:dual-spaces] for questions about [dual spaces](https://en.wikipedia.org/wiki/Dual_space) of vector spaces, linear normed spaces, etc. 

Perhaps it is worth mentioning in connection with this that there already exists tag called [tag:dual-pairs] which might be used [in context of functional analysis](https://en.wikipedia.org/wiki/Dual_pair). (But from the usage it seems that it is used in other meanings, too. The tag-info is empty at the moment.)