This tag should be used when discussing the nomenclature of places, peoples, events, etc.
If the question is purely linguistic, then it is probably out of scope for H:SE; judgement is required. The question should address toponymy in some historical context.
Questions about what a given place was called at a given time are important to the study of history, and would be in scope. (Bull Run vs Manassas is essential if you want to understand the Civil war; Bunker Hill vs Breeds Hill is trivial, but may assist in interpreting US Revolutionary War reports).
Questions about how a placename changes may be important to history or may illustrate history (Constantinople -> Istambul, Leningrad->Stalingrad, etc.)
Simple questions about why X is called Y with no historical context, are probably out of scope ("What did Detroit mean in the original Amerindian language?" is probably out of scope; "What is the etymology of Pennsylvania?" might be in scope. The first is an accident of history - the second is a choice that illustrates the plan of a historical figure.)