The Addressee option on the Results tab of the Customer Find Filter controls how the software will display the results of a Customer > Find. It also controls how they will be exported.

For example, let's say you had John Smith as the primary and his wife Mary Smith as the spouse. If you set Addressee to Spouse/Partner and then did a search for John Smith, the resulting customer list would only display Mary. If you instead set Addressee to Each Individually, both would be displayed.
See Customer Find Filter: Results Tab for more information.
To default the software to search by individual customers consider setting Addressee to Each Individually and make that the default option by clicking Presets > Set as Default.