MSM 

Mens sana in corpore sano*

- Juvenal (Satire X line 356)

 is a famous Latin quote meaning "A healthy (sound) mind in a healthy (sound) body".

The first two words, Mens Sana, mean A healthy(sound) mind, and is the mission of the Mens Sana Monographs.

Hence the name.

*For those who are curious, the phrase has been taken from a longer sentence ," Orandum est ut sit mens sana in corpore sano", which means, "You should pray for a healthy mind in a healthy body".

A worthy prayer, if ever there was one.