I'm keeping it pretty simple here, folks. What it is not is synthetic fragrances used in candles, incense sticks, room sprays, etc.
If you are a purist, you follow Gattefosse's definition that is is the use of the essential oils of plants, flowers, barks, and roots for therapeutic purposes. Gattefosse was a French perfume chemist, who, according to legend, in the early part of the 20th century, healed a burned hand by treating it with lavender oil. He went on to write extensively on the use of essential oils in healing.
If you are a non-purist, you also believe in the healing powers of incense, as demonstrated by the various Eastern religions that have used incense in their healing ceremonies for thousands of years. Others also believe that aromatherapy also encompasses the inhalation of fragrant essences in a natural setting, as a walk in a pine forest, enjoying a rose or flower garden, etc. The respiratory-clearing and emotion-enhancing effects are noticeable, and the person feels better because of the aromas.
Lately, the use of hydrosols, the waters left over from the distillation process that produces essential oils, has been adopted by many in the aromatherapy community as a healing medium. In the past, just rose and orange (neroli) waters were available, but today, everything from peppermint to thyme to helichrysum hydrosols are being bottled and sold, at high prices, for their supposed, unproven healing properties. For information on the potential dangers of hydrosols, mainly due to bacterial contamination, poor storage, etc., please see Martin Watt's discourse on the Lavender Cat website.
Practically all aromatherapy websites, especially those of suppliers, carries definitions of aromatherapy, so I encourage the reader to visit them if they wish a more extensive explanation. Those sites should also include all of the necessary warnings about essential oil safety, along with the usual outlandish claims of their use. I will allow the reader to make their own decisions as to the true definition of aromatherapy.
My first encounter (I now realize) was with Vicks-Vapo-Rub, a medicine close standby in the U.S. Vicks is nothing more than essential oils in a petroleum jelly base, and if anyone doubts my beliefs in the efficacy of essential oils, I would never dispute that the wonderful oils in Vicks got me through many childhood respiratory illnesses, speeding the healing process. In Europe, Olbas Oil was used in the same way, and Olbas also produces sports rubs, bath potions and other manners of conveying the helpful oils into the olfactory, respiratory and circulation systems of the person needing some relief.
Aromatherapy does work, but what I'm asking for, is research, proof and responsible statements on the part of the people now in the aromatherapy industry. They have, for too long, used glamorous, beauty industry-type hype to encourage people to use essential oils indiscriminately, and, perhaps dangerously.