Tren gym is not a term that is commonly used or recognized. However, "tren" is a short name for trenbolone, which is a powerful anabolic steroid that many bodybuilders and athletes use. Trenbolone is a man-made version of the hormone testosterone and can help people increase their strength, lose fat, and gain muscle. It is usually injected into the muscles or mixed with other anabolic steroids. Trenbolone works by copying natural hormones in the body that make muscles grow, such as testosterone and HGH. It is a type of testosterone, which is a male hormone, and it has other names like Tren, Trenbolone Acetate, and Trenbolone Hexahydrobenzylcarbonate. Trenbolone is illegal in the United States and several European and Asian countries.