Answered by Kristi Icaza
Each time you run a search, you get a set of search results. This particular set of results is given a results ID.
If you need to find that same set of documents again, use the results ID. Sometimes this is useful because rerunning the same search may yield different results, especially if new documents have been added or reviewed.
Do not use the results ID if you want to rerun the search and find all documents that match the search. To do that, either reconstruct the search, or if you saved the search, then run the saved search.
To view the results ID, open the Tools menu, click History > Results History, then hover over the number in the Total column.