MSDS stands for "Material Safety Data Sheet".
Manufacturers of items which contain hazardous/dangerous goods usually provide the above document which explains to shipping companies the nature of the hazard of their goods, how they should be packed and what documentation is required.
If we suspect that a package contains dangerous/hazardous goods we may ask for a copy of the MSDS to ensure we can comply with the shipping regulations. If you are unable to provide the relevant MSDS then we may be unable to ship your goods.