It is a transit phenomenon which occurs to every human being periodically. In transit when Saturn passes through 12th, 1st & 2nd Houses of one's natal Moon, it is called "Sadhe-Sati". As Saturn takes Two and half years to transit one sign (Rashi) ; it takes Seven and half years to travel 3 houses i.e. 12th, 1st, and 2nd. In Hindi we call Seven and half years as "Sadhe-Saati" so this specific transit period of Saturn is called "Sadhe-Sati".