Reducing the found set - also called find in find - is a very useful way to search within your current found set.
To search within your current found set:
Press the keyboard shortcut CTRL-F / CMD-F.
See Also
Finding data
Finding text (strings)
Finding numbers
Finding dates and times
Finding ranges of information
Finding data in related fields
Using multiple find criteria
Excluding records from your found set
Extending the found set