I have noticed that the tag duality is quite often used for questions about dual spaces in functional analysis and linear algebra. However, it's not immediately clear from the tag name that this is intended. (Although the current revision of the tag-excerpt explicitly mentions dual spaces.)

In addition to that, duality is a word which is used in several different - although related - meanings.

I suggest to create a separate tag dual-spaces for questions about dual spaces of vector spaces, linear normed spaces, etc.

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