You can use Last + [n] + [Days/Weeks/Months/Quarters/Years] to filter your data for a specified period of time going back a number of intervals. For example, if we are currently on October 15th:
Revenue Last 6 months will show revenue from April 1st till Sep 30th
Revenue Last 6 months include this month will show revenue from May 1st till October 31st
Revenue 6 months back will count 6 months from the today backwards: showing revenue from May 15th till October 14th
You can apply the same concept above on other date intervals such as years, quarters, weeks and days. See Date Filters for more information