A document providing detailed safety information on a particular chemical or substance. The MSDS will be a concise summary of all important properties and hazards of the substance, including not only the obvious, like flammability and toxicity, but also such points as mutagenicity, teratogenicity, and carcinogenicity. If you want to know how harmful or harmless something is, go look up the MSDS. They are required by law in the United States to be available in many situations.