Lab grown gems and synthetic gems are the same. They are made from synthetic materials, that were created in the lab. Synthetic materials have essentially the same optical, physical, and chemical properties as their mined counterpart. In all cases, stones must be referred to as “lab grown diamond”, “synthetic emerald,” “lab grown blue sapphire,” or “lab created ruby,” etc. In a word, lab grown gems are real gems. The only difference is that they are formed in the lab. Additionally, many growth methods exist to create lab-grown gems, such as flux, hydrothermal, Czochralski pulling, flame fusion, float zone, HPHT, and CVD. The growth cost of each method is different, so the price of each type of finished stone will have significant differences.   Imitation gems are simulants and artificial, which are man-made single-crystal products that are used to simulate appearance but not duplicate the characteristic properties of the mined gemstone they imitate. That is to say, imitation gems look like their mined counterparts. Imitation gems must be referred to as imitations when sold to consumers. Usually, they don’t exist naturally. For example, cubic zirconia is generally used as a diamond imitation, while green glass is an emerald imitation. Fake gems are counterfeit, which is specially made to cheat consumers. They don’t tell you what they are actually. For example, when someone sold a CZ as a mined diamond; and sold a red garnet as a ruby.