Essence

essence a term which, in a culinary context, is neatly defined by the NSOED as ‘A distillate or extract from a plant or medicinal substance, having its active constituents or characteristic properties in a concentrated form, … especially as an alcoholic solution of volatile substances.’ There are instances, e.g. essence of vanilla, where reputable firms market a product corresponding to this definition, but cheap imitations are also sold which do not.

Essential oils are not quite the same thing, but close. An essential oil is defined as a volatile oil obtained by distillation and having the characteristic odour of the plant etc. from which it is extracted. Familiar examples are oil of spearmint, oil of citronella.