Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called dry-cleaning fluid. It has a sweet odor detectable by most people at a concentration of 1 part per million (1 ppm). Worldwide production was about 1 megatonne in 1985.