Definition of a Neghbourhood
The neighborhood is the list of sites seen while browsing within one tab. The site's flags are shown in the footer.
Here some info on how neighbourhood works and what it has to do with the search.
When you reference other wikis in your page it creates a neighbourhood of wikis. It means that if you search for a page in a search box at the bottom of the Smallest Federated Wiki and have a page referencing other wikis you will be searching all pages within wikis you have referenced.
Here is Academies Neighbourhood - Smallest Federated Wikis of academies.