Extracts - Diluted oils, usually containing about 20% pure oils and the rest are additives. Alcohol is frequently used as an additive.
Pure Extracts are made from the botanical exclusively, and may only contain alcohol and water to dilute them into practical doses.
Natural Extracts are flavors that do not exist in nature, but are made by blending other Pure Extracts.
Flavors - Natural and artificial flavors are concocted when natural oil is not available for the flavor, and when an artificial enhancer works better with certain foods. Food-safe additives, possibly including alcohol, make up the bulk of the contents. Alcohol-free flavors must be used in the preparation of certain foods, like hard candies.
Natural Flavor Blends are made using all natural flavor ingredients that, in combination, emulate the desired flavor, but do not contain anything from the named botanical.
Natural flavors may contain diluting substances and emulsifiers such as synthetic alcohol, propylene glycol, and triacetin (a synthetic food grade emulsifier).
Essence, Oil, and Flavor are terms that are often used interchangeably, and that can mean an oil or an extract, or a concentrated substance. Check the ingredients to know for sure.