An Index Page is detailed activity view in a list form related to a particular feature. Index Pages list activity for Saved Queries, Lists, Pipelines, and Research Requests.
Below is an example from Lists and can be found under the 'Research Engine' category in the Sidebar.
On the right hand side of each column is a three dot menu that will allow you to take actions on a given List in this workspace:
We have enabled handy quick filters on all Index Pages to allow you to get to the information you need quickly. Click the 'Filter' button next to the Results at the top of the Index Page table to launch the Filter options. See more here: Index Page Filters