Some terms that describe herbal medicine types and methods along with anything else I think needs some explaining.
Decoction - A method of extracting substances by boiling herbal or plant material, which may include stems, roots, bark and rhizomes . Decoction involves first mashing and then boiling in water to extract oils, volatile organic compounds and other chemical substances. This method is used only when the plant material will not yield it's virtues using a more gentle method and the loss of volatile principles is not a concern.
Distillation - a process of separating the component substances from a liquid mixture by selective vaporization and condensation. Distillation may result in essentially complete separation (nearly pure components), or it may be a partial separation that increases the concentration of selected components of the mixture. In either case the process exploits differences in the volatility of mixture's components.
Elixir - A sweet-flavored liquid used for medicinal purposes often including alcohol.
Infusion - The process of extracting chemical compounds or flavors from plant material in a solvent such as water,oil or alcohol, by allowing the material to remain suspended in the solvent over time (a process often called steeping). An infusion is also the name for the resultant liquid.
Tincture - An alcoholic extract of plant or animal material. To qualify as an alcoholic tincture, the extract should have an ethanol percentage of at least 50–120 proof. Ethanol is able to dissolve substances which are less soluble in water, while at the same time the water content can dissolve the substances less soluble in ethanol. The alcohol content also acts as a preservative. Ethanol has a tendency to denature some organic compounds, rendering them so changed as to be ineffective.