Search Frequency Rank - What is the difference between Search Frequency Rank and Search Volume?

Search Frequency Rank is a specific numerical rank of a specific search term's popularity compared to other search terms during the given week.  This data comes directly from Amazon & Walmart retailers. 

Search Volume represents the number of times this search term was searched during the selected time period. This data is derived from a combination of known volume data and modeled proprietary volume data, and is only available for Amazon US. All search term searches made by the same customer session in a 24 hour time period will all be counted. Additionally, clicking on the next page of search results will be counted toward search volume.