Since Microsoft Search picks up just about anything on your sites, to get more specific results, you can tag documents. Think of it as similar to how Netflix categorizes movies by genre or release date so you can browse that specific category.
So you can search for “invoices FY2018” and get exactly what you’d expect.
To do something like this in your SharePoint, you first need to go to the document library in which you have your documents and add a new field that will hold that category.
In my case, for example, I created a new column of type [Choice] called "Fiscal Year." After I assigned each document a specific fiscal year, now I can group and filter documents based on this tag right in the library.
But what I can also now do, after the search picks up the new field, is to search for “invoices FY2018” and get specific results from anywhere on the site.