https://doi.org/10.1351/goldbook.H02908
Compounds having the structures $\ce{RS2H}$, $\ce{RS3H}$ ... $\ce{RSnH}$, in which $\ce{Sn}$ is a chain of sulfur atoms, and $\ce{R}$ is hydrocarbyl. Some people exclude hydrodisulfides from the class hydropolysulfides.