A Safety Data Sheet or SDS (formerly and still often referred to as a Material Safety Data Sheet or MSDS) contains structured safety information provided by the manufacturer or supplier of a chemical product. "A Safety Data Sheet, SDS, is designed to provide both workers and emergency personnel with the proper procedures for handling or working with a particular substance. SDS's include information such as physical data (melting point, boiling point, flash point etc.), toxicity, health effects, first aid, reactivity, storage, disposal, protective equipment, spill/leak procedures, and more." (ILPI FAQ)
The quality, completeness, and reliability of SDS vary widely. Don't rely solely on SDS for information that is critical to managing laboratory hazards and safety.
FINDING SDS: Most laboratory/specialty chemical suppliers provide free SDS on their catalog sites. You can also search Google for "sds" with the most-common name of the substance. It's a good idea to consult more than one data sheet for the substance, looking out for discrepancies and gaps.