ETS and related terminology
ETS stands for "environmental tobacco smoke", which is the preferred scientific term for this phenomenon. The word "environmental" distinguishes the smoke that is in the air from the concentrated smoke that is intentionally inhaled, a distinction that is obviously important (but absent from other scientific descriptors for smoke, like "diesel smoke", because it goes without saying in those cases). ETS is a combination of smoke from the burning tip of the cigarette when inhalation is not occurring and the fraction of smoke that is exhaled after a smoker takes a puff. These components can be called "sidestream smoke" and "exhaled smoke", respectively (with the modifier "tobacco" included if there is ambiguity in the context).
However, the latter is also often called "second hand smoke" (SHS) and this term it then often expanded to include all ETS, including the sidestream component. While SHS is a widely used term in popular discussions and often even appears in unbiased scientific analysis, it is not preferred terminology. That is not just because of the ambiguity (about whether it includes the sidestream component) but because "second hand smoke" was a term intentionally created for advocacy purposes. It is meant to evoke feelings of disgust among those for whom the phrase "second hand" evokes images of poverty, uncleanness, and violations of boundaries. While that built-in bias has largely faded in impact due to the common use of the term, it should still be recognized as being present.
A more recent term crafted for advocacy purposes, and that is fundamentally misleading to the point that it cannot be used in a genuine scientific context, is "passive smoking". This term, which refers to the experience of breathing ETS, was intentionally crafted to imply the (scientifically false) claim that breathing ETS is functionally equivalent to smoking. The term "passive" is also calculated to manipulate people's thinking; though technically defensible as the counterpart to "active", the common uses of the term result in it evoking notions of victimization and helplessness.
When evaluating writings that use these terms, use of "passive smoking" is a clear indication of an anti-scientific advocacy bias. The use of the somewhat awkward term "environmental tobacco smoke" indicates an effort to be scientifically precise or to avoid political language. "Second hand smoke" falls somewhere in between; despite its political origins, it has become the common popular terminology (as have translations thereof in languages other than English), and thus is often used in writing for a non-technical audience even when no political bias is intended.
