The Frequent Words feature can be found on the DC Setup page under "General Setup".
Words can be added by clicking on the 'add' button to the list of your choice. You can go to a different list by choosing another tab.
Duplicate Check has standard frequent words lists that can easily be applied to any field in your scenario.
Opening the Object in DC Setup and unfolding its Scenario let you see all frequent words list options that you can apply to the field.
Example:
If you are working with a lot of universities, it can be good to add the word University in your Frequent Words list.
Then when comparing 'University of New York' and 'University of Washington', Duplicate Check will only compare 'New York' with 'Washington' and see that is not a duplicate value.