What is the definition or description of: msm?

MSM: Methylsulfonylmethane is an organosulfur compound , present in many plants & foods & beverages, being marketed as a dietary supplement. Claims it helps immune system & stress.

Male/male sex: Men who have sex with men, or msm, is currently considered the appropriate way to describe male same sex sexual partners. There are plenty of men who don't self identify as "gay, " but who do have male sexual partners. I don't see this term used in popular culture, but rather it is used in the medical community, often when talking about risk factors for stds.