What is "sodium polysulfide"

Sodium polysulfide is a general term for salts with the formula Na S, where x = 2 to 5. The species S, called polysulfide anions, include disulfide (S), trisulfide (S), tetrasulfide (S), and pentasulfide (S). In principle, but not in practice, the chain lengths could be longer. The salts are dark red solids that dissolve in water to give highly alkaline and corrosive solutions. In air, these salts oxidize, and they evolve hydrogen sulfide by hydrolysis.