Selective Androgen Receptor Modulators (SARMs) are a type of therapeutic products that are having similar anabolic properties to Anabolic and Androgenic Steroids (AAS). However, SARMs do not produce same androgenic properties (these are causing male characteristics).
For example, synthetic testosterone (which is an anabolic steroid) binds to the androgen receptors and activates it. So does a SARM. However, the anabolic steroids are binding to androgen receptors in all tissues all over your body. This increases androgenic activity. SARMs, on the other hand, are selectively binding to androgen receptors only in specific tissues.
This greatly reduces risks of side effects while SARMs are still very likely to help with a variety of health conditions. So far, SARMs are for research purposes only.