This literally means "
peaceful sabbath" in Hebrew.
This is the standard greeting between Jews on Shabbat, from sundown on Friday until sundown on Saturday, but is often used as early as Thursday.
Shalom: peace/completeness or wholeness and general greeting for all time.
Shabbat: the seventh day of the week for the Jewish calendar. A day off (literally a day to be set apart from all other days-for introspection, spiritual growth, and renewal) - beginning on Friday at sundown and ending on Saturday evening when three stars appear in the sky and can be viewed together.