At the moment there are 42 questions tagged rotating and 18 questions tagged sideways. (6 questions feature both tags.) rotating is used for for the general concept of rotating (with the help, of. e.g., macros from the
graphicx package) as well as for questions about the
rotating package and its
sidewaystable environments. For the latter, sometimes the sideways tag is used additionally or instead. I propose to make sideways a synonym of rotating and to merge the existings tags/questions.
Note that there is also the landscape tag which is used for questions about changing paper orientation from portrait to landscape. Although there's some overlapping with rotating, I think landscape is warranted as a separate tag.