Sarms are selective androgen receptor modulators. Androgens are a class of hormones that serve as ligands that bind to cellular androgen receptors. In a way, they offer muscle-building properties through this binding to the androgen receptor.
A drug that can either block or stimulate the same nuclear hormone is called a selective receptor modulator.
In simple terms, Sarms mimic the actions of anabolic steroids and pro-hormones to offer their bodybuilding properties, yet, they are not steroids.
They target selectively on the muscles and bones without giving the user unwanted side effects, unlike steroids.