Aromatherapy Oils is just a marketing term. Often enough, sadly enough, these aren't even oils that you should use, because most of them are (very) inpure and should not be used in the purpose of therapy through oils, in which form whatsoever. The best thing these offer is a fragrance so that it smells good in your house, just like those boxes or blocks you can find in the general store to place on your toilet so that it smells good.
Essential oils are pure oils that are used for therapy through aroma's, either applied with a carrier oil on the skin, evaporated with a aromalamp or inhaled through adding some drops of pure essential oil to a bowl of hot water. Even here, inpure forms are available.
But the biggest difference between these 2 will be the price: aromatherapy oils will cost significantly less then essential oils. The process of extracting essential oils is tricky and uses experience, time, precision and specific tools. The cheap stuff isn't even an extraction of material from plants or herbs, it's synthetic stuff... which explains the cheap price.
Learning aromatherapy myself. I'm no expert at all, but I like to be fair towards myself and my customers. My oils are very expensive, but they are pure. Only took me a long time to find a good store and a good course, but it was worth it.