For questions about the alchemist, a class or character focused on the use of alchemy, typically to create magical or quasi-magical potions.
Alchemy in games is patterned after the real-life proto-science of the same name. Some alchemists performed great experiments still recognized as major contributions to the hard science of chemistry, while others were philosophers and mystics; most probably were a blend of both. Various major historical figures dabbled in, or were obsessed with, various alchemical pursuits, the best known of which include the transmutation of lead into gold, and the creation of an elixir that allowed immortality. Both endeavors were often said to rely on the creation of the philosopher's stone.
In games that have actual, functioning magic, alchemists often do not have real magic, at least in the spellcasting sense. Instead, they use a mixture of herbalism, chemistry, and just a pinch of true magic to produce the various alchemical items that they employ. Potions and oils are very common, as are unstable concoctions that explode when thrown at a target.
This tag should be applied to questions about alchemists, either a class, or as a character archetype. It should not be used on questions about alchemy in general, particularly as available to all classes; for such questions the alchemy tag should be used.