Sade Sati is the passage of Saturn through the natal moon. During this period, the planet Saturn passes 3 signs (the sign where your Moon is in the chart, one before and next of the moon) and is held in each and every one and a half years. Together, his journey takes seven and a half years, and this is Sade Sati's literal translation.
Planet Saturn teaches us through restrictions, denials and burdens, so this period of time for an individual can be quite difficult if we are not taught about its effects. It is a period when we need to make a "deep and effective cleaning" in our lives - to abandon the old patterns that limit us and make room for the new one. How to proceed during this period, however, helps the advice of a person who interprets Jyotish.